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So my novel setting is a pseudo-European continent that is at a Renaissance level of technology, and over the past century has experienced rampant sea level rise. I’d imagine that this would present a massive challenge in terms of people having to move, large cities and centers of trade and art drowning, and political unrest as a result of the environmental shift. But as I thought more about it, I realized that it’s likely that many kingdoms and other power brokers would be willing to invest time, money, and manpower into things such as dams, some sort of large drainage system, and efforts into saving things like structures of historical importance and holy places.

This brings me to the idea of an Atlantis style dome, which would be in maybe 50 ft of water, and would reach a height of 50 feet above the waves. I haven’t fleshed it out fully yet, but I’m imagining that in it, there’s a cathedral or monument important enough to the people/culture of the area to merit saving.

Would such a structure be possible, given the technology of the time? If not, what are some plausible ways to get close to this idea, or to save the important site in another way?

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  • $\begingroup$ I think they'd have a harder problem making it watertight. 50ft. of water isn't that much pressure - even glass can take that. $\endgroup$
    – Halfthawed
    Oct 8 '19 at 2:55
  • $\begingroup$ I see. I had thought that glass wouldn't be able to handle that much pressure. As for making it watertight, I'd imagine some large scale application of the techniques used on ships in the time period would be the best bet. $\endgroup$
    – user2532642
    Oct 8 '19 at 7:25
  • $\begingroup$ I imagine that, were it important enough, they'd have people on site if possible, to remove any water that makes it through the barrier. If it is completely submerged, making it possible for workers to get to and from the site might be an additional challenge. $\endgroup$
    – CAE Jones
    Oct 8 '19 at 12:05
  • $\begingroup$ Not really answering your question, rather an idea: In a scenario with less foresight I'd imagine people would start building barriers, hoping it's enough. How would they know how long waterlevels remain high. And as waterlevels rise the barriers would be built onto, rising, rising, rising, until they have a large amorph wall around a complex of structures, or a round cylinder around a building, open on top. After people are sure sealevel is stable and stays so for a while, people could seal them with a dome of glass. They could even build floating bridges to connect the areas. $\endgroup$
    – Backup Plan
    Oct 8 '19 at 12:47
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    $\begingroup$ Isn't the Netherlands basically a renaissance-built undersea dome? It doesn't have a top (yet) because the sea hasn't come up high enough (yet) but in principle it's kind of the same thing, right? Sorta, kinda? $\endgroup$
    – workerjoe
    Oct 8 '19 at 14:39
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Large domes would have been possible to construct during this period. In fact very large domes were constructed much earlier. The dome in the Pantheon in Rome was built around 126CE and is a free standing dome 43m across and 43m high.

It would be impossible to have any significant glazing on such a dome as the art of glass making would not have been sufficiently advanced to provide quality uniform strong glass and I doubt that had such material been available they would have been able to seal the glass properly.

However there are two big problems. The first is the nature of the ground the structure is built on. It would have to be bed rock (or bed rock would have to be near the surface) otherwise the hydrostatic pressure of 50 feet of water would probably cause seepage and erosion below the foundations.

The second problem is that of the weight of water on the dome. Domes like the Pantheon can sustain their own weight but adding thousands of tons of water would probably be too much to bear.

An alternative approach would be to build a large dam around the artefact facing outward. Perhaps stone blocks jointed with pitch might be used. There would still be seepage so multiple windmill and or animal power pumps would be needed to keep the water out and would need to be multi stage as well as the pressure would be greater than one atmosphere at 50 feet.

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  • $\begingroup$ They could simply use quartz crystal instead of glass $\endgroup$
    – nzaman
    Oct 8 '19 at 15:44
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    $\begingroup$ Except they would not be able to seal the quartz crystals into the support structure any better than with glass and quartz crystal is not that common, does not come in very large size crystals and is extreamly hard to cut. $\endgroup$
    – Slarty
    Oct 8 '19 at 19:17
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The largest dome built during Renaissance belongs to the church of Santa Maria del Fiore, and has been designed by Brunelleschi.

With its 45 meter (144 ft) internal diameter and 55 meter external diameter is the showcase of the masonry of the times.

Dimension-wise what you ask is surely feasible, though the entire building process is not exactly understood nowadays.

The additional challenge is posed by the laying ground, on which you give no specs, and from the underwater building.

If the laying ground is muddy and not stable it is probably unfeasible, if it is rocky it might be possible.

Depleting such a large volume of water for the entire duration of the building process might also be a challenge bordering impossibility, for the technology of the times.

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  • $\begingroup$ I didn’t think about the ground’s specs at all, but I’ll be going with the idea that it’s solid rock, to make it more feasible. $\endgroup$
    – user2532642
    Oct 8 '19 at 17:54

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