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In my fantasy novel, I have people living in a giant swamp forest. The swamp stretches as far as the eye can see, so draining is not an option, as there is simply nowhere to drain the swamp to.

My people need to have a city in this swamp. This city isn't some rundown village; it's a big city, capable of supporting several thousand people at least. It is the capitol of an empire.

The problem with having such a large and magnificent city in a swamp is the lack of solid material to build it on. Most of the ground is underwater, or likely muddy and not suitable as a base for buildings. There might also be flooding, which would change the water level, making it nearly impossible to build anything that doesn't float. Stones wouldn't be overly plentiful.

How could a giant city be constructed in a swamp? How would they get around possible flooding? What would they build their city on?

Notes:

  • These people will have access to abundant trees, animals, and even a limited amount of iron ore, as that can sometimes be found in swamps. They do NOT have access to stones (unless those are plentiful in swamps - which I don't believe they are).
  • The technology level of these people is Roman Empire. A lot of what they might build is limited by the lack of stone.
  • Before you cite New Orleans as the answer, consider that these people do not have access to the pumps which keep New Orleans dry. Limited dikes, yes. But only what they build up out of mud and lumber.
  • I do not live near a swamp, so my knowledge of them is limited to what I have heard. If my assumptions are wrong, please let me know.
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    $\begingroup$ Why don't the people of your city import good building stone from elsewhere? They are on a waterway. Moving large stones by water is relatively easy. $\endgroup$ – sphennings May 24 '17 at 19:54
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    $\begingroup$ Iron ore is stone. $\endgroup$ – user25818 May 24 '17 at 20:13
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    $\begingroup$ "When I first came here, this was all swamp. Everyone said I was daft to build a castle on a swamp, but I built in all the same, just to show them. It sank into the swamp. So I built a second one. That sank into the swamp. So I built a third. That burned down, fell over, then sank into the swamp. But the fourth one stayed up. And that's what you're going to get, Lad, the strongest castle in all of England." ~King Of the Swamp $\endgroup$ – user2389345436357 May 24 '17 at 20:56
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    $\begingroup$ You may find some helpful information in the answers to this similar question: worldbuilding.stackexchange.com/questions/78570/… $\endgroup$ – Cody May 24 '17 at 22:27
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    $\begingroup$ @user2389345436357 Don't forget the "huge... tracts of land" $\endgroup$ – Cody May 24 '17 at 22:30
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Such a city has been already built in reality, and it was even the capital of an empire: Venice

The buildings of Venice are constructed on closely spaced wooden piles. Most of these piles are still intact after centuries of submersion. The foundations rest on plates of Istrian limestone placed on top of the piles, and buildings of brick or stone sit above these footings. The piles penetrate a softer layer of sand and mud until they reach a much harder layer of compressed clay.

Submerged by water, in oxygen-poor conditions, wood does not decay as rapidly as on the surface.

This gives you good indications on how to build such a city.

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    $\begingroup$ Same with the Aztec city, it was built so well they had huge stone pyramids on it. $\endgroup$ – Kilisi May 25 '17 at 10:40
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    $\begingroup$ Also, St Petersburg, at enourmous human cost: independent.co.uk/news/world/europe/… $\endgroup$ – pjc50 May 25 '17 at 15:48
  • $\begingroup$ Also a extensive swamp don't necessary excludes small hills here there where you can build. Also you can move earth form nearby regions. Two examples off extensive swampy regions with lots of towns: Everglades and Pantanal $\endgroup$ – jean May 25 '17 at 17:54
  • $\begingroup$ Note that when Venice was built, the lagoon was saliter then today. This helped to preserve the lumber. Rotting piles due to sweeter water are one of the problems Venice is facing today. $\endgroup$ – mart May 26 '17 at 11:39
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A Floating City

You said it yourself, with flooding and an unstable earthen base on which to build, structures have to float. So make them float, using pontoons build from huge hollowed-out trees like massive canoes.

Height will be limited, and most structures will likely have to remain roughly pyramid-shaped to maintain stability. Your city will be very horizontal, sprawling throughout the swamp, but not very high. Tides and floods will raise your city.

You can create floating boardwalks for foot traffic and have drawbridges to allow boat traffic through the area. Anchor your buildings with heavy stones or to the surrounding trees. Use canals and dikes to direct water flow.

A good, real-world example to look into would be Tenochtitlan, the capital of the Aztec Empire in Mexico, which sprawled out from an island in Lake Texcoco.

A Raised City

If a floating city doesn't suit your world or your people, build your city in the trees of your swamp forest. Your city will be more vertically integrated than a floating city, with structures climbing up the trees before extending outward to the next one.

Suspend buildings and bridges from upper branches and anchor them to the trees themselves or with weights dropped into the swamp.

Use cantilevers to extend platforms from the trees (or between the trees) on which to build your buildings. Instead of boardwalks and causeways, you'll have rope bridges and ladders (or elevators).

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    $\begingroup$ A floating city, you say? $\endgroup$ – Mike.C.Ford May 25 '17 at 11:45
  • $\begingroup$ +1 for Raised city among the trees. Assuming that the forest stretches "forever", wood supply shouldn't be a problem. $\endgroup$ – SGR May 25 '17 at 13:19
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I would consider looking at the Aztecs who created the city of Tenochtitlan in marshland at the edge of a lake. At its height it had a population of 400,000 people and was the Capital of the Aztec Empire. They in order to create it they constructed a series of artificial islands and linked them with causeways.

These islands were created using a system called Chinampa were areas of swamp were fenced off and layers of mud, lake sediment and rotting vegetation were layered together a series of canals enabled canoes to travel between different areas.

In other parts of the world artificial islands have been created in swamps by weaving together reeds or tree branches and covering these with soil taken from the swamp.

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You could go with a floating city but that's a lot of wood in contact with the water.

You can minimize the wood contact with the water by building the city on pitch soaked pylons (maybe even copper clad). Each building would be build independently with hanging walkways between them and hinged ramps or rope ladders to floating docks under the buildings. The trouble is that wood rots very well in a swamp. So the pylons would have to be easily replaceable. Replacement would have to happen less often the better protected the pylons are (hence the pitch, creosote, or cladding).

Possibly have wealthy or powerful people use imported stone for their pylons.

The size of the city will be limited because they will eventually deforest the swamp if it is too large. That's why imported stone would be the best solution for a long term city. Maybe only the outer/newer buildings will have wood pylons. Or maybe a slum with rotting pylons that they scavenged from building replacing old pylons.

I picture the first step of wealth being building half stone half wood pylons (just enough stone to hold the wood out of the water most of the time). Then, eventually, have all stone. The half pylons would bean that you can replace two rotting pylons for the price of one (cut the pylon in half to place on the stone). This would be an investment in the long term cost savings for the family. Building the stone up to a full pylon is one pylon that would "never" (for at least a few generations) have to be replaced. That will protect the family from future hard times.

This would also allow people to see how wealthy a family is, just by looking at the pylons.

Another problem with a large settlement in the swamp will be food. If there is some crop that can float on the water, grow in the water, or grow in shallow water, that would be good. Otherwise, they'll run out of fish in the local area.

Also, think of why they are there. What can they get there that they can't get somewhere else that has easier living conditions?

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    $\begingroup$ Wood actually holds up quite well when submerged under anoxic conditions. Also, rice and taro are both suitable staple crops that require marshy conditions to grow. $\endgroup$ – Shalvenay May 24 '17 at 21:25
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    $\begingroup$ So I've found out here. However that water/air interface where the wet wood in in contact with the air is still in danger. I guess it means that they have the added expense of digging the old pylon out after it has rotted away at the water's surface. That still supports half stone or all stone I think. A floating city would still be in danger. I remember an old wooden dock that was listing to the side pretty good before we replaced it with one that had foam floats. $\endgroup$ – ShadoCat May 24 '17 at 22:35
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    $\begingroup$ You can use wood under water, or over water, you just need something else for inbetween. $\endgroup$ – Paŭlo Ebermann May 25 '17 at 22:19
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stone may or may not be common in a swamp, it depends on the swamp.

The most common construction technique you see in swamps is to build on stilts. wood is plentiful so they build out of that. If stone is common you can build from stone and wood anchor pilings like venice. Water travel becomes the main way to get around that and foot bridges. You may want to look at venice for inspiration on layout if not construction. It is not that stone is hard to find in swamps as much as it tends to shift and sink into the muck. So you can decide which way you want to build.

Clean water is difficult, you either need to boil water to drink of have pipes to drill deep wells.

flooding tends to be only bad once people start building levees to redirect water (it concentrates flooding instead of letting it spread out over a large area), if natural flooding cycles are allowed and people build on stilts only the most extreme storm flooding will bother anyone.
Keep in mind new orleans was a city before it had pumps, they just tended to build on the high ground.

some stilt villages can be quite extensive. enter image description here

enter image description here

The real issue you have to consider is where they get food from. farming swampland requires reshaping it, the aztec "floating" farms (Chinampa) or Bangladesh floating farms are both good ways. Or if your swamp is a little drier rice patties.

A lot will depend on how self sufficient you want it to be.

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  • $\begingroup$ Yes. Race patties are faster than normal rice patties! Ha! $\endgroup$ – ozone May 24 '17 at 21:53
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The important references for you are the Aztecs and the Khmer both of which built an empire so are entirely appropriate for you to use. Also St. Petersburg and Venice are good one city examples.

The Aztecs as others have mentioned built artificial islands by collecting the mud and supporting it with wood pilings. They could build large islands suitable for buildings and smaller ones suited for agriculture.

Such islands have very good agricultural productivity so this would give you the food production needed for large cities and an entire empire. The high productivity is due to excellent irrigation given by the surrounding swamp and due to the mud used to build the islands being rich in nutrients. Once the nutrients get depleted, the islands is simply demolished and a new one built from fresh mud. This system avoids most issues other forms of agriculture have with the soil quality degrading over time.

I think the natural progression of architecture would be: Huts made from reeds or mud brick for commoners. Painted and decorated mud brick and wood for the wealthy and important. Imported stone for the public buildings to prove the power of the state. The stone buildings would be on larger and more stable islands and have actual basements to stop them from sinking. You should also use vaulted construction to make buildings less massive for their size. That said the carrying capacity of such ground is mostly a matter of using enough wood pilings and question said "abundant wood".

Concrete is also something to consider. It makes building large structures easier and, in theory, allows building large structures that float in the water. Although I do not think anyone actually did that before modern aircraft carriers. But you could, if you have lots of good concrete. The Romans probably could have done it and they are what you gave as technology level reference...

The Khmer were the other reference I gave. What you should copy from them is their use of waterways. They used an extensive system of canals to connect a large plain for easy transport and to supply irrigation for large area of water intensive agriculture.

You do not need extra irrigation, but the canals would supply an efficient transport system capable of, for example, transporting large blocks of stone huge distances for your building projects. Dredging canals would also be a natural source of mud for your artificial islands. There is natural symmetry between digging navigable canals and building artificial islands that would make your empire quite efficient. And of course the easy transport of food would allow the cities to grow much bigger.

The canals would also provide water level control if you add some locks to them. And you really should as this level of control would hugely improve your resistance to both drought and flooding. The nature would still be able to overwhelm the system, but usually droughts or floods would result from mismanagement r corruption letting the system fall into disrepair.

Easy ways to get drinking water are collecting rain water and filtration. (Aztecs built an aqueduct, which Cortez then cut.) Constant rain is kind of annoying so I guess the best solution would be to let your people build filtered wells on their artificial islands. You could also have the people drink drinks such as beer or wine which contain alcohol that kills bacteria and thus store better than water. Personally I would probably just make my state more powerful by giving it control of large cisterns. I find "Be a good citizen or drink sewage!" appealing for some reason.

That said alcohol does have some attractive properties as well. Namely alcohol (or vinegar) not only store themselves, they can also be used to store foods that would otherwise not store well. Storage in alcohol or vinegar can also replace cooking and allow the swamp people save valuable and scarce wood. I mean even if the question said "abundant wood", the wood would not stay abundant long if the swamp is filled with people constantly burning wood. So heavy use of alcohol might be used to explain why the heartland of your empire still has lots of wood.

EDIT:

Important note on the consequences of this type of construction. This requires large scale planning and coordination to work. As such there would be large bureaucracy managing the canals, the locks, and the artificial islands. If all agricultural land is produced by large scale construction linked to upkeep of canals performed by the state, then the state will control all agricultural land and by extension almost all of available food. They will also control all trade along the canals.

So the likely outcome would be a state permeated by a monolithic centralized bureaucracy. Which might not be what is wanted.

You can avoid this by being earlier in the evolution of the system.

It starts with the individual villages building artificial islands for agriculture. Then some villages grow into centers of trade and people start building larger islands for them and improving the connecting water ways. At that point communal decision making by villages is not enough and city based bureaucracy is born. After an empire is born the bureaucracies are combined and gain the capability to build improved canals and manage the water level. Which is a big benefit to having an empire. After this the centralized bureaucracy will start taking over the control villages have over land.

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  • $\begingroup$ "So the likely outcome would be a state permeated by a monolithic centralized bureaucracy. Which might not be what is wanted." Fortunately this fits with the story just fine. An excellent answer, thank you! $\endgroup$ – Thomas Reinstate Monica Myron May 25 '17 at 15:02
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Crannog

The celts built Crannogs or artificial islands on lakes and lived on them for protection from wild animals and marauding people.

They would drop stones and wood over the same spot in the water, eventually building a small island. Over generations the Islands would be enlarged.

There really is no limit to the size, especially if you've a shallow swamp and have access to lots of stone and/or fire-hardened timber.

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Wooden ships. You can build on the hulks of wooden ships. There are a lot of ships under San Francisco as shown in this map.

from http://www.upout.com/blog/san-francisco-3/map-shows-ships-buried-underneath-san-francisco-2 enter image description here

It made news when they discovered an old sailing ship under the ruins of the World Trade Center. Wooden boats were apparently used for landfill not infrequently.

from http://www.huffingtonpost.com/2014/07/30/world-trade-center-ship-mystery_n_5634280.html enter image description here

There is nothing wrong with your swamp city built on heaps of wood. Cut down the forest, pile it up and build on it. It would be more interesting to have it be built on an abandoned fleet of some sort. Wood rots but buried wood can last a long time in the anaerobic environment.

Ceramic Your people don't have stone, but they have mud and they have wood. They can make bricks. They can make ceramics. The Romans made both in abundance.

https://en.wikipedia.org/wiki/Monte_Testaccio Monte Testaccio is a large hill built entirely of discarded Roman ceramic jugs.

It has a circumference of nearly a kilometer (0.6 mi) and stands 35 meters (115 ft) high, though it was probably considerably higher in ancient times

That is pretty cool. A dedicated brickworks and a giant stack of bricks should be doable in your swamp. I learned about tells on the worldbuilding stack a few weeks ago. They are big. They are mostly old mud bricks.

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