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This question is part of a series that includes mosquito prevention and agriculture.

The environment is a rain forest basin, similar in many ways to both the Amazon and the Congo. There is a mighty river and its many tributaries that flood every year, raising and lowering the water level 10-15 meters each year. In this basin, a river civilization develops to a Bronze Age level.

Edit: Editing to add more about the nature of the floodplains. This environment is like a varzea, a flooded rainforest environment. The flood levels are much higher than and not comparable to any river other than the Amazon. There is almost no topographic variation (hills) and in the rainy season dense jungle covers all the available dry land. The people are restricted to the river, and the grassy parts of the flood plain, all of which are under 10m or more of water in the wet season.

I imagine that this civilization will have to go to extraordinary measures to build and maintain cities. In order to keep the city high and dry all year, the city could be built on a 20m platform of limestone blocks. For example, the bases of eight Great Pyramids would provide a limestone surface of about half a square kilometer, perhaps enough for a city of 5,000.

You can assume that limestone can be quarried near the headwaters of one of the river's tributaries and is then easily transported by water to anywhere on the river network.

Is it feasible to build and maintain a city of half a square kilometer in these conditions (i.e. with the erosion of a massive regularly flooding river)? How big of a city could be reasonably made? What sort of innovations would these city dwellers need to make to keep their city livable?

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  • $\begingroup$ Have a look at New Orleans. Or many cities in the midwest on the Missouri or Mississippi rivers...lots of cities are built on flood plains. Grand Forks ND is another one. $\endgroup$ – James Mar 9 '17 at 21:25
  • $\begingroup$ @James Not as many cities are hit with yearly 15m floods though. $\endgroup$ – kingledion Mar 9 '17 at 21:39
  • $\begingroup$ Just to clarify, is your city build on a network of architectural stilts, or on one big solid platform? $\endgroup$ – cobaltduck Mar 9 '17 at 21:50
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    $\begingroup$ Venice (in Italy) seems to be surviving pretty well. Suggest looking into it's history and building practices. $\endgroup$ – Catalyst Mar 10 '17 at 9:31
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    $\begingroup$ Check out the Halligen and Warften / terps. Islands only just above sea level which are regularly flooded. Homesteads and sometimes small villages are built on Warften / terps, mounds (~15m high) to be safe from floods. Instead of one massive platform you could do something similar with your city being built on a collection of platforms (from whatever material). $\endgroup$ – hsan Mar 10 '17 at 10:21
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I think stone platforms would only be used for special buildings such as palaces, temples, or mausoleums under your scenario. The elevated platform would be an integral part of the architecture of the building. This might extend to ceremonial centers, which are essentially collections of such special buildings having larger platforms shared by multiple buildings, so there might be one or two cities with parts such as you describe.

But for ordinary cities, buildings and people using stone does not make sense. They would use raise buildings by stilts or by collecting earth as village mounds. Village mounds would have retaining walls of wood or stone (depending on location, wealth, and direction of flood currents) and the earth would be compressed by use and as part of mound construction.

The earth would come from the canals and ponds needed to support your floating farms. You need constant water access during flood and drought and that requires moving lots of earth for the needed waterworks.

The result would be an extensive network of small agricultural villages surrounded by ponds filled with floating gardens and connected with a network of canals. There would be few ceremonial centers for religion and administration which would have extensive public buildings complete with stone platforms.

The best source for such civilization is probably the Khmer Empire. Their water intensive form of agriculture was rice paddies not floating gardens so the network of irrigation canals was more complex and the actual farms less complex.

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There are a couple of things which are going to make it difficult for your people to make massive stone structures.

1: Lack of manpower. A lot of manpower is needed to make big stone structures (Maya, Aztec, Egyptian, Cambodian). That kind of manpower means a big population. Big population means big agriculture, which means a lot of arable land. If your folks are confined to the river their population will not be big.

2: Lack of stone. Having local stone is crucial. The quarries for these ancient structures can be seen from the structures. Mayans built with stone in the jungle but there were hills to cut the stone from. You describe an environment with no hills, which means no rock outcroppings or cliffs. Everything will be uniformly covered with deep sediment. I am thinking that a quarry not much higher than the river will run into the water table very fast. The ancient Amazonians built but not with stone.

Stonehenge stones came from a distance. All the stones in Stonehenge stacked on top of each other would make a pretty puny pyramid. The idea of a Stonehenge type structure serving as the base of a wooden building is pretty cool, but the tallest stones are maybe 6 meters.

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  • $\begingroup$ The idea about the stone, at least, is that it can be floated from great distances along the river. That is how the Pyramid's stones came hundreds of miles downriver from upper Egypt. $\endgroup$ – kingledion Mar 10 '17 at 0:09
  • $\begingroup$ I do not think that is right about the pyramids. This link shows the view of the Great Pyramid from the quarry next to it. aeraweb.org/gpmp-project/great-pyramid-quarry $\endgroup$ – Willk Mar 10 '17 at 1:23
  • $\begingroup$ You are right. The granite for some interior components came from upriver, but the vast bulk of limestone came from right there. theglobaleducationproject.org/egypt/studyguide/6stone.php $\endgroup$ – kingledion Mar 10 '17 at 1:37
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Is it feasible to build and maintain a city?

Oh, yes, this can be done. It's a lot of work and you don't need stone at all... Setting it in a tropical area is the new part (*edit: for me).

In fiction: March to the Sea has a city in a flood plain with a lot of water. I think the city was called Diaspra.

For the Exterior:

In real life: the Netherlands. They have fought long and hard with water. Of particular interest would be flood control. With your 15 meters of water you will want to scale it up a bit, but you will gain an idea about the amount of work... And you don't even need stone:

Popular in the Middle Ages were wierdijken, earth dikes with a protective layer of seaweed. An earth embankment was cut vertically on the sea-facing side. Seaweed was then stacked against this edge, held into place with poles. Compression and rotting processes resulted in a solid residue that proved very effective against wave action and they needed very little maintenance. In places where seaweed was unavailable other materials such as reeds or wicker mats were used.

Just don't forget some big sluices and a way to get rid of the water during the raining season. Mills could work nicely if the winds are not to bad. Maybe use water mills? Otherwise you just have a new lake that took a lot of work.

It seems the Babylonians had some ways to get water to hi-er parts. The Hanging Gardens seem to be able to do so. There are ideas how they did it. But we are talking water screw technology. And that is extremely hi tech for their age. Think space shuttle when it first flew.

For the Interior:

Having a lot of water is good, helps with hygiene and transport. Look at Amsterdam's layout, very useful to transport stuff without carts or beast of burden. As an other answer said, Venice is famous for their canals.

There are more then these European examples; Angkor Wat. It seems it had very good water management (pdf) systems.

But stagnant water is very dangerous with disease and critters. And this being a tropical environment you might want to do something about big water predators. On the other hand, you have river dolphins to play with. Oh, the options. (never mind the (giant) otters)

As said in other answers, you will need a lot of people to make and hold dikes, but you surely can. They will just be very big.

note: most of these cities were build with more then bronze age tech, so it will not be simple.

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Manpower and foundations

The vast manpower requirement has been mentioned, but the foundations required will need major maintenance during the dry season.

For an example of what I mean, put a rock on a sandy beach in front of the incoming tide. How long does it take before the water undercuts your rock and it sinks into the sand? Not long at all.

Your foundations will either require you to dig down to bedrock or dig down deep enough that the currents over the course of the wet season do not undercut your perimeter stones. In the dry season you'll need to rebuild and refill what has been cut away, especially at any the corners where the effect will be amplified by turbulence.

This is not a city that will long stand the test of time without regular maintenance.

Venice is lighter than what you're considering here. It's built of brick on raised ground with wooden piles to stabilise the ground below the foundations. The city is only 600 years old and requires constant maintenance.

The Dutch prefer to keep all the water out, reducing their exposure to the erosion that moving water causes. Their maintenance is equivalent to yours, while over a much larger area, it's still focused on a perimeter.

I would consider following these examples: Start with a waterproofed stone perimeter, fill the inside with rubble and mud stabilised with wooden piles then build on that. This will reduce your manpower requirement to build the city down to something possibly manageable, however no matter what you do you will need to maintain that perimeter. Moving water is a relentless and unforgiving opponent.

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Egypt co-existed with the Nile's annual floods (and indeed, depended on them) for maybe 5000 years, until the building of the Aswan Dam. (In the 1960s IIRC). So yes, it's quite possible.

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  • $\begingroup$ The Egyptian city sites were several meters above flood level. There is nothing comparable available in my forest, see the edit to the question. $\endgroup$ – kingledion Mar 9 '17 at 22:06
  • $\begingroup$ @kingledion: Then why build a city there? Though even as I ask, I realize I have an answer: unscrupulous developers. We've been having a rather wet winter hereabouts (after a decade or more of dry to drought), and a bunch of "dry" lakes aren't dry any more. Unfortunately, in the intervening years, developers built houses on that nice flat land. $\endgroup$ – jamesqf Mar 10 '17 at 18:37
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I see no problem with this city, unless floods are so violent that they can overturn the stone blocks.

After each flood, blocks will get tilted and shifted. This is Ok if the citizens would immediately go to work and get the blocks fixed. They would benefit from anchoring those blocks with piles driven deep into the ground and invention of cement.

But if your city is left without maintenance for a while, its existence would be put into question.

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  • $\begingroup$ Not so sure they can repair the platform well enough though, they could patch it up but I think after a 50-100 floods it might become unstable. $\endgroup$ – Ovi Mar 9 '17 at 22:00
  • $\begingroup$ I assume the original technology that was used to set up those platforms is not lost. If they can't repair, they should replace. $\endgroup$ – Alexander Mar 9 '17 at 22:11
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    $\begingroup$ @Alexander There is a difference between knowing how to cut and stack stones, and being able to get underneath a massive city-sized construction which has some elements tilting with subsidence or irregular erosion. The difficulty in accessing the lower stones, much less working around the water table and dealing with the enormous weight bearing down on them from the truly gargantuan construction on top of it... this would be a serious engineering challenge even for modern construction. $\endgroup$ – pluckedkiwi Mar 10 '17 at 13:58
  • $\begingroup$ @pluckedkiwi - if that is the case, then yes, but I would consider that a fatal flow in design. City should be constructed in a way that each stone block can be serviced individually. $\endgroup$ – Alexander Mar 10 '17 at 17:06
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    $\begingroup$ @Alexander they would need to deconstruct whole sections of the city to excavate the lower base stones. Remember, this platform is to be stacked so high it is at least 20 meters above the level of the surrounding soil (to say nothing of how far down it needs to go to be stable) - that is a lot of courses of stonework. Think about trying to fix some of the stones of the bottom layer because the muddy ground under it has been shifting a bit, when that bottom layer is under 25ish meters of stonework. I suppose you could just keep reshaping/releveling the top and hope nothing collapses... $\endgroup$ – pluckedkiwi Mar 10 '17 at 21:58
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It is entirely possible to build cities on flood plains. Giant stone blocks would definitely work, but wouldn't be the first method used.

First off I would expect some hills or higher ground to exist in most all floodplains, this is where the longer term structures of a city would likely be built. These hills could be expanded and linked, either by earthmoving or with large stone blocks as you suggest. This would likely be the basis for why a city exists here at all, people could live here during flood season and a city is born.

Some structures could be built on stilts, pilings, or otherwise be tall enough to be above the flood waters, these types of piling structures are very common for most coastal cities as they expand onto the water and would be likely to show up in a river port city as well. These have the advantage of not requiring anywhere near as much effort to construct, and can be built piecemeal and develop organically as the city grows. Your stone structures could also grow out of this process as some buildings build large stone foundations.

A large number of structures, including those of the poor would likely be built on the lowest and least desirable ground and would simply not be built to last and would be washed away each year and have to be rebuilt each season.

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As @Will mentioned, stone structures would require significant manpower, which this area is pretty much designed to eliminate.

The physics check out - You CAN build on top of stone blocks and have a city get flooded under, around, etc regularly. Venice, Italy is a good example of something like this being possible, if a bit extreme.

The answer you need now is not "Can it be done?" but "How was/is it done?" How do these people feed everyone? Fishing is a good start, but there's only so many fish. Do they trade with other people up and down the river? If so, then what do they trade? Is the stone of theirs of very good quality? Do they have good masons? Do they sell their fish - Perhaps one kind that only breeds around them is considered a delicacy in the town up the river.

There's a lot more that needs to be answered - and asked - to truly solve this question.

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  • $\begingroup$ Assume that agriculture intensive. The floating farms question I linked provides some details. Between dry season farming on terra firma wet season floating farms, and fishing, the agricultural productivity is as high as in any river valley civilization. $\endgroup$ – kingledion Mar 10 '17 at 0:14
  • $\begingroup$ Floating would also require significant infrastructure to build. It would allow for the city to exist once they're complete, but it still asks how were they built? Did the people settle here with ships, and turn those ships into the first floating farms? Did there used to be some "Protected" areas that are now city, and floating farms were built as the land was built on? $\endgroup$ – Andon Mar 10 '17 at 0:18
  • $\begingroup$ Oh! Also, bear in mind soil depletion will mean these "Floating Farms" will have some problems, especially with some crops. A floating farm will also not gain the benefits of floods (Nice, fresh nutrients). These are things to take into account as well. $\endgroup$ – Andon Mar 10 '17 at 0:24
  • $\begingroup$ If you have comments about floating farms, you should answer or comment on that post. This is for city building :) $\endgroup$ – kingledion Mar 10 '17 at 0:24

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