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Modern international trade basically runs on standardized shipping containers and the infrastructure developed to handle them. Looking at just a small part of it, using crane to unload full containers and move directly from ship deck to truck bed, or vice-versa, and allowing containers to be packed in a space-filling arrangement on deck, is just way more efficient than individually packing items in a ship's hold or truck trailer, isolating the complex bits of loading and unloading to only the very ends of the transport chain.

But... modern shipping container infrastructure basically depends on access to large quantities of cheap metal--for the containers, and the enormous port cranes that handle them.

It seems to me that an analogous system could have been developed significantly earlier in history, however, using wooden crates of standardized size (much like we still use standardized wooden pallets), and smaller-scale wooden cranes. In reality, wooden harbor cranes have been in use at least since the Middle Ages in Europe--and if they got the idea to use a bridge as the basis of a gantry crane, they probably could have gotten a lot bigger than they actually did! And cranes more generally go back to 1500 BC.

Unfortunately, according to Wikipedia "Crates had been used for many years without a clear origin in documented history. Modern crates from the early 20th century demonstrate a very evolved technology already considering practical and economic considerations built into crate designs." I can't imagine building a crate would really pose any problem for a Medieval carpenter, or even an ancient Mesopotamian one.

So, just how far back, and at what material technological level, would the development of something like the modern system of standardized container shipping have been possible to develop? (Say, if a time traveler went back and gave someone the idea.)

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    $\begingroup$ without steel you can't make ships that you can efficiently put containers in, people have ot pack crates in the hold so standardization ins not all that useful. $\endgroup$
    – John
    Sep 13 at 0:05
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    $\begingroup$ @John You can stack crates on a flat-decked catamaran. That's literally stone-age technology which was sufficient to colonize the Pacific. $\endgroup$ Sep 13 at 1:56
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    $\begingroup$ "without steel you can't make ships that you can efficiently put containers in" – of course you can.... people put containers in ships for years..... I can't believe any argument that says it's IMPOSSIBLE for a Bronze Age civilisation to agree that all goods be put in one-cubit-by-one-cubit crates, loaded on to ships, off ships, onto wagons. That is obviously POSSIBLE. $\endgroup$
    – Humphrey
    Sep 13 at 1:58
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    $\begingroup$ You don’t need cheap metal for shipping containers to be worthwhile, you need expensive labour. If most people are working in subsistence agriculture, the cost of a dock worker won’t be very high, so it’s not worth investing to save labour costs. $\endgroup$
    – Mike Scott
    Sep 13 at 14:11
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    $\begingroup$ The advantage of containers boils down to two things: 1) automated loading and unloading, and 2) not having to re-pack when transferring from one form of shipping to another. To leverage (1) you need a means of automation for loading/unloading. To take advantage of (2) you need to a) frequently need to transfer cargo from one shipping transport form to another and b) have standardized containers and standardized shipment forms (vehicle-holds) that can efficiently carry them. You also need a lot of volume to justify all of this. Doesn't work in a world of cheap labor and low volumes. $\endgroup$ Sep 13 at 15:54

12 Answers 12

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There are a number of requirements to make efficient container shipping happen:

  • The labor cost for handling freight exceeds the cost for transporting packaging. Big ships and their fuel and crews are cheaper than gangs of stevedores.
  • Ships and trucks can be designed for a few large shipping crates: large hatches over much of the deck space. Straight bulkheads without protruding frames. That goes against the design requirements for wooden hulls and for masts and rigging.
  • Containers can be built to standard sizes. This requires standard measurements, which were historically not available: Will a crate from one artisan really fit into the wagon bed from another artisan or does it require fitting?

There were pretty standard sizes of amphora and barrel, but these were for liquid where containers were a necessity.

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    $\begingroup$ IMHO the "standard measures" thing is the key here. The metric system was introduced in the 18th century, and the meter was de facto an artifact standard (i.e. defined in terms of a specific physical object, rather than something you can independently reproduce) right up until SI standardization in 1960(!). Before that point, if you wanted to know how long a meter was, you basically had to ask for a copy of the meter and hope somebody was willing to give it to you. Hilariously enough, this was still true of the kilogram right up to 2019. $\endgroup$
    – Kevin
    Sep 13 at 7:16
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    $\begingroup$ It would be easy enough for a king/committee to cut 100 planks the same length, send them to the 100 ports/provinces, and declare that the standard. I feel like people are really overthinking the question, which is essentially whether there are technical obstacles to building a bunch of boxes. Obviously there are no technical obstacles to building a bunch of boxes. $\endgroup$
    – Humphrey
    Sep 13 at 8:20
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    $\begingroup$ "Big ships and their fuel and crews are [in that world] cheaper than gangs of stevedores" - this is the best example why this is mostly an economical and not technological question. Even as late as the mid 20th century, it was common even in developed nations for vagrants and people from poorhouses to go to the docks, and be collected by company representatives for one-off jobs to load or unload a ship, usually by carrying the cargo in sacks on their back, for money barely enough to cover that day's food. It's only the prosperity of modern times which makes us rely on mechanized unloading. $\endgroup$
    – vsz
    Sep 13 at 11:56
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    $\begingroup$ @CSM their advantage is that they're intermodal: they go ship to train to truck (or to wagon and river barge) in one piece without being repacked $\endgroup$
    – Humphrey
    Sep 13 at 12:33
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    $\begingroup$ @John You don't need it to be accurate to the picometer. You just need them to stack together reasonably well. Your measuring tool also doesn't need to be wooden, and you don't need that many generations of measuring tools (you could even make all of your in use measuring tools directly from your reference measuring tool, but even a third or fourth generation tool is probably fine, as long as care was given while making it). $\endgroup$ Sep 14 at 20:21
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As I recall, shipwrecks show that standardized amphora were used. The ship was built with a raised platform of carefully spaced holes for the first row, and subsequent rows stacked on top of that due to their shape.

Everything from wine to sand was shipped in these amphora.

They were standardized containers with the ship specially constructed to handle them. But they were small, being individually man-portable.

Also, look at barrels. A barrel is a container that is also a tool: It can be rolled, and furthermore rolled along a narrow plank. Then, it can be stood on end again by rocking it to build up the amplitude.

Many different goods were placed in barrels, using them as general purpose boxes.

I can imagine a culture evolving from amphora that were sized to be the largest that a longshoreman can readily carry, to being lifted by overhead crane out of a hold that opens as a vertical shaft from the deck rather than going down stairs and ramps. They could keep the same distinctive shape, and rely on that for the grabbing mechanism; they would just be much bigger, and continue growing in size as the cranes replaced human labor.

Another issue is how to moving them around the dockyards. Unloading a ship is one thing; but you have to then move a huge mass around to warehouses and eventually to delivery. Rails or canals around the dockyard might let them move such masses around; but modern containers are integrated, turning into a semitrailer for surface delivery. Without that ability, you save time unloading the ship but still need to break down the large containers close to the unloading site in order to continue.

You might find that the equivalent to a modern pallet size is optimal, and perhaps a super-pallet puts 2×3 on a platform and stacks them 2 tall as well, so 12 pallets are lifted and loaded at one time by the crane. This is also an easy way to evolve the concept and incrementally implement it: standard pallets with hand-jacks and mobile cranes (in the role of modern forklifts) get established everywhere including surface transport (wagons) and warehousing. Those get bundled together into super-pallets as crane technology improves and ship design changes to use top-loading cargo holds. These are easily broken down again at the boundary where the super-pallets are no longer supported, whether that's along the shore, the destination warehouse, or depends on the surface cargo carrier.

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It's not a technical problem. As you say, anyone could build a crate.

It's an organisational problem: getting everyone to agree on the standard.

Basically in any worldbuilding scenario, it's fine to just declare that there are standardised containers. What organisational systems exist in your society? They decided to standardise containers. This is plausible in Mesopotamia, medieval Europe, whatever.

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    $\begingroup$ @John they won't have to unpack and repack them to move them onto chariots. $\endgroup$
    – user253751
    Sep 13 at 8:05
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    $\begingroup$ 1 chariots were not used to move cargo, 2 they did not need to unpack them to put them on wagons before, the slow part of shipping was getting cargo on and off the ship which is no faster with this. $\endgroup$
    – John
    Sep 13 at 9:31
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    $\begingroup$ yes I did mean wagons. $\endgroup$
    – user253751
    Sep 13 at 11:03
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    $\begingroup$ @John The advantage here is more one of inventory management than ease of transport. If you are dealing with objects of a uniform size and shape, then a standardised transport/storage container that fits exactly X of that object in way that can be visually confirmed by just opening the lid is huge for improving the efficiency of transactions involving that object (consider that in modern times it’s not unusual for inventory to be measured by ‘pallet’, ‘crate’, or ‘box’ for exactly this reason). $\endgroup$ Sep 13 at 11:12
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    $\begingroup$ @John, it would be hugely faster to load a ship. Ancient cargo cranes could lift about 3 tons; so, you are talking about the difference about 50 crane loads that take 4 people to lift or 3000 amphoras that take 2 people to load by hand. That is ~30 times less labor... probably even better than that though since a crane can just swing and top load it whereas amphora required carrying in onto the ship, down the stairs and all the way to the shelf it belongs on. $\endgroup$
    – Nosajimiki
    Sep 13 at 18:12
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An analogous system was developed much earlier in history - the barrel:

Around 350 BC they were already using watertight, barrel-shaped wooden containers that were able to withstand stress and could be rolled and stacked. For nearly 2,000 years, barrels were the most convenient form of shipping or storage container for those who could afford them. All kinds of bulk goods, from nails to gold coins, were stored in them.

...

The use of barrels for the transportation of bulk goods slowly lost its importance in the 20th century with the introduction of pallet-based logistics and containerization. However, they are still of great importance in the aging of wines and spirits.

The thing is, a modern container ship can rely on modern infrastructure being present at any given port; that was not the case before modern telecommunications, navigation and mechanization.

Before the industrial era, there was always the chance a ship might show up to port and need to be unloaded by hand via manual labor. Barrels are perfect for this: they'll roll or stack depending on how you orient them, and a single barrel is easily maneuvered by a two man team.

If you have more infrastructure, great! It'll go faster. If you don't, that's fine - you can still get your ship unloaded.

There's no way in heck you're moving a full container (or large crate) with manpower alone, at least not without a whole lot of pulleys and other equipment.

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    $\begingroup$ This is a great point because until relatively recently, there was a massive difference in the level of infrastructure between ports. You couldn't count on anything in particular being available, so as a fallback any system has to function using nothing more than brute manpower. $\endgroup$
    – bta
    Sep 14 at 19:34
  • $\begingroup$ The OP specifically assumes a civilization that uses cranes in its ports. Ports prioritize having cranes more now because shipping containers require them, if an ancient civilization had shipping crates, then thier ports would have more reason to install cranes. You would probably start off with shipping containers just on major trade routes. Then as other ports could afford the cost of a crane, they would build them to attract more trade until they become ubiquitous like they are today. $\endgroup$
    – Nosajimiki
    Sep 15 at 15:28
  • $\begingroup$ Before modern navigational tools, there was a decent chance that any given ship wouldn't hit the port it's aiming for, and would instead arrive at a port in the general vicinity. Being able to unload and restock regardless of conditions in the arrival port was pretty important. $\endgroup$
    – Tacroy
    Sep 15 at 16:35
  • $\begingroup$ @Tacroy Before modern navigation tools, ships did not go in straight lines. Greek and Roman trading ships stayed within eye site of shore and followed written lists of landmarks called periploi. If a storm ever blew them out of sight of shore, they could just head back in the right general direction following the sun and stars until they hit the shore line, then keep following it until they hit thier next landmark to confirm thier position. In this way, it was very rare for them to ever get more than a couple of miles off course. $\endgroup$
    – Nosajimiki
    Sep 15 at 22:03
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Base it off of a Cart Capacity of Grain In Ancient Rome

A lot of answers on how it was done, but not how it could be done. Grain was by far one of the most large scale transported materials. It was also one of the least dense; so, if you design your containers to transport grain, then anything more dense will still work without leaving your with a container that is unnecessarily light for other common goods. So, if you wanted to transport Oil or Wine for example, you could still hit the shipping container's weight capacity by loading it with something like amphoras, barrels, or wineskins. You could even load it up with lots of smaller crates for easier unpacking where required.

The average single draft horse can pull about 3600kg. Since we are talking about shipping containers, your carts themselves could be a basic flatbed cart like a bray which can be made pretty light weight. So let's say your actual, fully loaded cargo container is 3200kg on a 300kg cart. The average density of grain is about 0.79g/cm^3 meaning your container should have a volume of ~4,000,000 cm^3.

Interestingly enough, the Roman Polyspaston crane used for loading and unloading ships is estimated to have a lift capacity of about 3 tons; so, it seems that the Romans were already designing thier port cranes to lift cargo by the single draft-horse cart load; so, you could use the cranes that already existed in the ancient time period, but the containers mean a lot less loading and unloading would be required between the cargo's origin and destination.

Thanks to the width of a horses backside, most Roman carts had wheels about 144cm apart. These carts wore ruts into commonly used paths making paths untraversable by carts of other sizes; so, Romans, and most Medieval civilizations that followed, standardized thier carts to a wheel width of about 144cm. Subtract about 8cm for room for wheel spacing and tolerance, and the ideal width of a pre-modern cargo container should be about 136cm. If you were to make it as tall as it is wide, then the total dimensions of your cargo container would be about 136 x 136 x 216 cm.

So, your ships could pull into port, off-load with a kind of crane that was already common, and place the container directly onto a cart to be carried away. If you have a 2 horse cart which was more common for moving things around inside of cities where roads are wider and paved, it can actually pull 3 containers with fewer horses; so, you could turn the containers up right or sideways to make them fit, or you could even create a larger 136 x 216 x 408cm standard "triple crate", but this would require much bigger cranes; so, probably not the best idea except in certain high-traffic trading situations where you can count on bigger 10 ton cranes on both ends of the trip. Most Roman cargo ships held about 2000-3000 amphora with each amphora weighing about 50kg. But by using shipping containers instead; such a ship could be loaded with about 32-47 containers of the same weight dramatically reducing time spent carrying amphoras around and reducing the space needed to carry it all.

enter image description here

What About Materials

Industrial metal production did not exist in the ancient world, but industrial lumber production did. Roman Sawmills were comparable to the sawmills of the Early Industrial Revolution allowing them to turn out significant amounts of boards and plywood making processed lumber surprisingly cheap. So, while making giant shipping crates like this may be cost prohibitive in most of the Ancient and Medieval world, in the Roman Empire, wooden vessels could have been made much more cheaply than the ceramic ones they used. Most likely, they preferred amphora because round containers are much easier to make with ceramics than wood meaning the amphora could be rolled... but since these crates don't need to be moved by hand, this is not a factor.

As for water proofing to keep your goods dry, this is also very easy using Roman technology. When the Romans needed to water proof wood, they would coat it with a resin made from boiled pine sap. This resin is both cheap, and durable making your crates able to survive many years of direct exposure to rain and sun.

What About the Rigging or Stability?

Having done an in depth look at many different images of Roman medium cargo ships, I've come to the following design to show the most likely layout of lines on a typical Roman Oneraia (grain ship) while in port. From what I can tell, an Oneraia has enough accessible deck space for ~50 cargo containers which could be stacked 3 high without interfering with the sails or two high to not even come above the top deck or even 1 high and still give the ship about the same cargo capacity as a traditional amphora trade vessel for a total weight of 160-480 tons of cargo... well over the 100-150 tons of amphora they could normally fit using racks. Since it is unlikely that such a ship could even safely transport crates more than 1 or 2 high, this gives the ship more than enough crane accessible space to load it to its maximum capacity despite some of the top deck being inaccessible due to riggings. Since you do not need to load the ship any higher than an amphora transport to get well beyond the ship's max weight, you can count on the ship remaining stable and buoyant. This also means you could cap the bays with closable doors if you so choose allowing your to not have to sacrifice any deck space and help keep the rain out of your bays. Or more simply, you can lay out your deck to line up with the crates making the crates become your deck.

enter image description here

What About the Structural Concerns of Open Cargo Bays?

While some concern has been voiced about having large open bays, many Greek and Roman ships were already designed like this. On larger wooden ships, it is the beams and not the deck that gives the hull integrity; so, this just means you need to space your beams some increment of just over 216cm apart, and then you can lower the crates between them. Even on the smaller trading ship shown below, there is enough room to fit 2 crates high without going so high as to make the ship or containers unstable.

enter image description here

How do These Crates Improve Shipping?

In a normal Roman Cargo ship, you start off by having to fill amphora, barrels, sacks, etc. into increments of 30-50kg. (That is about 65-105 items you need to move to fill a draft cart). Amphora were also quite heavy. An 11kg amphora only holds about 39 liters which means that an amphora grain ship spends about 25% of its tonnage on the shipping containers themselves. In contrast, a shipping crate of this size weighs about 180kg meaning your container weight is just under 5% of your load. So, a 150 ton crate ship would carry 30 more tons of grain than a 150 ton amphora ship.

Also, those containers need to be loaded 1 at a time onto a cart, often requiring 2 people if you need to carry the load more than a few feet to your destination. The wagon is then driven to a port where the cargo is unloaded 1 container at a time into a loading net. The loading net is then hoisted by crane onto the ship where you then need to unload them 1 at a time into thier proper racks. Then when you reach your destination, you have to repeat the whole process in reverse to get the human portable containers back onto carts which are then brought to the destination where the cart must again be unloaded 1 item at a time. This means that your little amphora or what not has to be carried 6 times to get from point A to point B. If we assume that each time you move an amphora by hand that it takes you an average of 3 minutes (these things are heavy and require careful handling after all), then the total labor cost spend on loading time for a single wagon load of goods could easily be 20-40 hours (That is ~940-1880 man hours for a 150 ton ship.)

By using shipping containers, you can put most cargo like grain directly into the crate saving tons of time and money on packaging, but even if you do need to transport something like wine or oil, you can still fit 3200kg of them into the container in other vessels since these liquids are more dense than grain. Romans often preferred wine skins over amphora when it did not need to go into a boat because they were so much lighter, but did not handle shipping as well; so, chances are amphora would go out of style if you could keep wine and oil skins safer in transit with a crate, meaning you'd still save on weight per goods. Since loading the container is just as easy as loading a normal wagon, the worst case scenario is you break even on labor for loading your initial cart, but for cargo that you can put straight into the container, you can save time and materials by using one big box instead of lots of little ones. Then when you reach the port you are going to, you just hook your crane to the top of your container and hoist it straight off of your cart and onto the ship trading ~7-14 hours of hard labor for what will take a 4 man team just a few minutes. Then you get to the the destination port and lift the crate straight onto the next cart that brings it to the destination where you can unload the crate. So instead of having to load/unload 6 times, you only have to do it twice reducing your labor costs by about 14-28 hours per shipment per container (~725-1250 man hours for a 150 ton ship). Given how cheaply Romans could make such a crate, I'd imagine it could pay for itself in just a few trips.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Monty Wild
    Sep 15 at 14:13
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The impetus towards standardized shipping crates isn't ships; the impetus is mechanized land transportation like trucks and trains. There may be a slight advantage towards regular-shaped crates on board a ship, but crews have been lading irregular materials onto ships for millennia without much trouble. But when crates are carried away from ships on wagons or sledges standardization is moot. Animals can only pull so much weight, every item is headed to its immediate destination, and nothing is large enough to worry about transit obstacles.

With the invention of railroads and trucking, shipping doesn't stop at the water's edge. Items need to be offloaded onto trains, carried to distribution centers, then offloaded onto trucks to head towards final destinations. Standardized containers ensure that:

  • Items can easily and seamlessly be attached to rail cars and truck beds
  • All items will pass properly through railway cuts, tunnels, underpasses, and other land obstacles
  • Items can be sorted by destination at the beginning of the journey, not at each stage of the journey, improving logistics
  • Items are enclosed and anonymized, reducing casual damage and theft

While standardized crates could be achieved as far back in history as one likes — and I'm quite sure that it was within certain contexts, such as barrel construction (where consistency of liquid volume was important) — there's no real advantage to it until land transportation can move items in bulk as well. It would be a solution for a problem that doesn't yet exist.

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  • $\begingroup$ Considering that the first standardized shipping container was driven by Malcom McLean while running a shipping company(Sealand), This was after he seld off a trucking company. $\endgroup$ Sep 13 at 21:44
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Assuming you are talking about stacking the containers on deck as on a modern container ship, the technological cutoff date is more or less 1850. Use of sail is prohibited, since the vessel heels too much, and you'd get containers falling off. Furthermore, it's hard to make wooden cases sufficiently waterproof to handle the long (multiple months in some cases) voyages exposed to both weather and salt water spray.

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I believe the main problem to solve is large enough usable open cargo deck.

Modern container ship is basically a box without top with several partitions holding its shape. That allows to put cargo as low as possible starting well below the water level. (Some images can be found at https://www.sciencedirect.com/topics/engineering/container-ship)

With wooden ships achieving such a box shape is not possible with technologies we had so far. You basically have two types of ships that worked - relatively small ships without deck (like traditional Viking's ships, row boats and all sorts of river barges) and bigger ships that are essentially tubes build with wooden circles (flattened a bit for the deck) spaced 1-3 feet apart covered with wooden boards outside to make the hull and the deck.

So for smaller open-desk ships you can put some box-shaped containers low enough to not cause ship to flip sideways... but it is unlikely to be beneficial enough due to small size an inability to stack containers.

Bigger ships indeed can have decent size cargo hold but it had to be accessed via relatively small openings in the deck. Cutting more than couple of deck beams in a row to make an opening would require way too much reinforcement. If you look at any picture of such ship you'd see that cargo openings normally are somewhat squares at most 1/3 of the deck width and spaced far enough to avoid weakening structure too much. As result loading anything below deck requires moving items quite far from the opening accessible by crane. And there no way to load anything on the deck itself as it would be too high above the water making ship too unstable.

So wood as the only material to build a ship makes using boxes (as opposed to barrels) very inconvenient.

Couple other points to consider:

  • sailing and rowing ships have a lot of people on board. All those people already got all they time payed for (or forced) so there is no particular need to make process more efficient from the point of view of number of people involved. Port side workforce was not too expensive either to my understanding.
  • barrels are far superior to boxes of any kind to be moved by a person in tight spaces of irregular shape. Due to its shape it can be turned on a dime and rolled in any direction relatively easy. Dragging or pushing rough wooden box on a rough wooden surface is not an easy exercise.
  • barrels are easier to fit into round hull of wooden ship, require less precision in manufacturing (it will naturally try to be round in case of minor mistakes unlike with boxes 90 degrees corners is not an angle that wood (or almost all structural materials) will hold.

So you need iron/steel to have decent size openings in the deck to make loading actually easier and non-sail-based power to actually benefit from smaller number of people required to load the ship - 1850 suggested in some other answer seem to be a reasonable time for when it may be viable.

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  • $\begingroup$ What about catamarans? You can build a multi-hull boat with a large flat deck low to water with stone age technology. $\endgroup$ Sep 14 at 15:35
  • $\begingroup$ @LoganR.Kearsley you can easily build raft but connecting 2 hulls with sea worthy wooden connection alone is hard... Getting that connection to be high enough to not work as a sea anchor but low profile enough to not work as a sail... is just impossible irrespective of materials you have access to. $\endgroup$ Sep 14 at 18:16
  • $\begingroup$ I think the Polynesians would disagree with that assessment, given that they did in fact build such vessels, which were seaworthy enough to cross the Pacific on. $\endgroup$ Sep 14 at 20:03
  • $\begingroup$ @LoganR.Kearsley they also could not be loaded with much weight. and are tiny on the ship scale. $\endgroup$
    – John
    Sep 14 at 21:48
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    $\begingroup$ The Tessarakonteres, the, largest ship built in the ancient world, was a catamaran... not that the Tessarakonteres was a practical ship, but it did prove that it can be done at very large scales. $\endgroup$
    – Nosajimiki
    Sep 15 at 1:00
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Other answers are good, but they all miss the point about larger cranes. One or 2 mention how much weight they can handle, but not about interference. And by that, I mean the sails of the ship.

In order to avoid interference of an overhead gantry crane, you need to build it very tall. You have to build it so tall that you can accommodate every ship, even the tallest masts (which I can't find any actual measurements of). This costs money, lots of it, since you have to do more reinforcements as you go higher and even need more rope to handle the cargo. (If you have a 10:1 block and tackle to handle heavy loads, you'll need 10 ft. of rope for every 1 ft. extra height to the crane. If you add 100 ft. to the height of the crane, you need 1000 more ft. of rope. And that doesn't include guide ropes.)

It's much simpler and cheaper to build a crane that rotates out over the ship deck, a cantilever or jib crane. This also helps avoid accidental swinging of the cargo into a mast, since the shorter rope would be more controlled in wind than a long rope. One of the reasons we can manage this today is the high precision of the metal rails, bearings, and motors used. Back before electricity, it was all manpower or animals to move these cranes, and that generally doesn't have high precision when it comes to moving heavy objects on wooden or stone rails.

In today's reality, docks and ships still use cantilever cranes. A gantry crane is only used when the center beam can be supported on both sides. These are used on docks, but generally not to load ships, but rather to stack containers on dry ground. The massive cranes used to load supercargo ships are a hybrid of cantilever and gantry cranes. They span a road for loading and unloading, so are considered gantry cranes, but the side that loads the ship is actually a cantilever.

Also, the cargo ships of today don't use sails, so you don't have to deal with that interference. And the massive weight of today's full containers help make it less likely they will be affected by wind.

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    $\begingroup$ When you look at most pre-renaissance cargo ships, they only had 1 tall mast, most that had a second sail was more in front of the ship than above it; so, you only needed a couple of meters of clearance to swing a crane over it. Also, most of the rigging that crisscrosses a sailboat is just tied to the mast while in port; so, they would not be there to get in the way during loading anyway This means that a relatively short crane can reach nearly the entire deck. $\endgroup$
    – Nosajimiki
    Sep 15 at 16:04
  • $\begingroup$ You forget another thing about a classical crane: I only has one axis. This means you either have to put the train on rails (not really feasible for a wooden man-powered crane.) or you can unload at a single point of the ship. $\endgroup$
    – Sebastian
    Sep 16 at 21:13
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I find the answers mentioned to be sufficient - though I might provide a plausible scenario in which this could arise. In the past, there have been notable empires such as Rome. There have also been non-political empires, like the trade empire of the Phoenicians.

I could definitely see that in this sort of context one of these large groups decides on a standard of having shipping containers. I could see many possible scenarios where this could arise if you thought up sufficient reasoning for it. Maybe these crates started out as a higher standard for more valuable cargo, and it was found that it worked great for all the other cargo as well.

Maybe the trading involved is between different partners working on a gigantic engineering project, and they are searching for ways to make the process of building more efficient.

All in all, I think this is a cool idea to add flavor to a story.

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Big customers set the rules to sell to them.

Be a large customer, determine the desired "crate" shape, demand that shape, refuse business to anybody who does not conform to that crate shape.

This will likely result in several "standard" crate shapes.

Next step is for several large customers to agree on the standard for their purchasing block. This will eventually evolve in to several standard crate sizes.

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  • $\begingroup$ And the biggest customer will often be the government. $\endgroup$ Sep 16 at 8:00
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But then, how do you move the pallet?

OK, so you've come up with a nifty design for containerized handling dockside. You have moved a 4500 pound/2000 kg pallet of goods from the boat to the medieval wagon. What happens next?

No one has a fork lift.

The wagon can't travel in the dark, medieval wagons don't have headlights. Assuming you did this in the morning, you have the rest of the day and the range of the horses to get the wagon to a destination or SAFE layover. And this will tie up the entire wagon.

The moment you change vehicles or unload to get the wagon back... or reach your destination... you will not have a crane at those locations. So you will be forced to "break bulk" - hand unload the cargo by the bag or shovel full.

So this somewhat defeats the purpose of containerization. The issue being that material handling equipment like fork lifts aren't ubiquitous.

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  • $\begingroup$ perhaps the wagon will have a way to simply drop the pallet at the destination, like a dump truck. If the standard crate was longer than it is tall (as with Nosajimiki's Answer) it could slide out of the tilted bed. $\endgroup$
    – JDługosz
    Sep 15 at 16:05
  • $\begingroup$ Places you would need to bring goods that are not already in smaller packages inside the crate would be proto-industrial anyway. In the ancient world, this would be places like water mills, lime kilns, ceramic workshops, etc. These are places that are already heavily invested in mechanization; so, adding the cost of a basic movable lever crane or trestle hoist to lift crates on and off of carts would be minimal compared to the infrastructure they already used. $\endgroup$
    – Nosajimiki
    Sep 15 at 16:18
  • $\begingroup$ Something similar to this: margawalt.com/wp-content/uploads/2016/10/Th2_lift1.jpg could be made using purely Roman technology and move several ton crates around a warehouse just like a forklift or pallet jack does. $\endgroup$
    – Nosajimiki
    Sep 15 at 16:24

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