How would cities be built on large ruins?

Question

Basic background

The cosmic entities that forged the world got a little more than they bargained for. Even the most powerful of them were but limited aspects of the underlying magic of the cosmos. The world they created, and the races they blew life into are not so limited. In particular, the sapient races of this planet carry within them a more prefect blend of these aspects than the gods have, though they have far less power. As a result, after years of bowing to the gods' ever more cumbersome and capricious rule, they rebelled, and wielding an aspect of destruction alien to the ruling deities, they killed them off. Humanity was left with the ruins.

And onto the question:

So we're now left in a world with massive edifices the gods built to house themselves. Lets assume they're made well enough to stay standing for at least a few centuries, aren't so big they just crush through the planet's crust, but are made of materials that humans can work.

Humanity has a vested interest in building its ruling cities in these places, as the ambient magic proves useful for the ruling mages. Further, they don't want to destroy the ruins completely for fear of the same fading.

So, what do these cities look like, how do they grow? Lets suppose that most god-dwelling contain a few spires, some sweeping walls, and sit atop a nice plateau. Most of the internal rooms will be far too big for a human to use as a single space unless they are using it as some sort of large open square/marketplace/field/park.

How do you build inside a building?

Technology/Magic levels:

The main inhabitants of the upper cities are in a roughly Early Modern technology level. Largely pre-gunpowder and steam (though a part of this is societal taboo, so other areas may be better along). However the nations they rule are non-magical and are in more of an early industrial stage, so they may have some benefits of this (Again though, taboo segregates)

Magic is plentiful, if somewhat dangerous. It is shipped in bulk as a magical mist/condensate from certain areas where large numbers of gods died in the rebellion of mankind. When properly channeled it could be used to achieve large projects such as levitating large objects/bulk material and stengthening or enchanting building supplies.

Answer 1

Many cities were built on the remains of older cities, and indeed the mark of ancient cities is often a hill or mound where the earth has finally blown over and covered the final layer of the city. Troy is perhaps the best known example, but these mounds exist throughout the near and middle east.

I have the feeling the normal human fear of disturbing the dead/awakening unknown powers would have kept the population well away for the first few centuries, until the tradition faded from history to fable. The new cities would then be built on the top of a low mound, with the more impressive structures rising half buried from the earth. The new rulers would incorporate these pieces as part of whatever new palaces, temples or other structures they wanted to build, so an ancient tower would have new walls coming off at whatever angles supported the scheme the royal architect had in mind.

Since you did not specify size, I am imagining rather outsized buildings, so the ruins would not be fully incorporated into the new city, perhaps two or three new structures might be built on the recycled remains of the older one. For the buildings that have fallen into ruin, their foundations would serve much the same purpose, and the fallen stonework would become the walls and towers of the new buildings.

This leaves some interesting issues for the new inhabitants. Since the city is built on the partially buried remains of an older city, there might be tunnels and passageways under the new city which are not clearly mapped or defined. Skillful thieves, assassins and spies would be constantly working underground to try to determine the layout and how this could be used for their purposes. Ordinary people might also seek out surviving underground structures, for use as cheap housing or ways to evade the taxman or royal guard.

And of course since this is a magical setting, items of power might still be concealed somewhere in the old remains (doubly so, since the hiding places are now in rooms hidden under the new city.) The people of the city might also be less than keen on people burrowing away underground, since that might awaken ancient magic, and the rulers would also be less than keen since they could be taken by surprise from underground. Periodically, the King sends the Royal Guard below ground to sweep the area, roust out people and block the more threatening passageways. A special corps of mining engineers might be in the ruler's employ for this purpose as well, or perhaps a select group of small guardsman adept at moving and fighting in confide spaces.

So the new city will be built on a hill around a seemingly random collection of old towers and walls with new structures attached to them. The city will be a hive of activity, both the normal day to day activities above ground, and a much more furtive existence underground.

Answer 2

Considering that your god-corpses are effectively mana-batteries, and your gods are said to be all powerful, we can assume that they probably build things out of conjured unobtainium.

Why? Well if the gods are very large creatures (as hinted in the large sweeping spaces paragraph) quarrying out enough regular stone to make cities their size is going to make alot of large holes in the ground and require an astonishing amount of labour. On the other hand, of course, this could be exactly the sort of tyranny your humans may have rebelled against? Who knows?

The problem, therefore, is how easy is it to work with the materials of your ruins?

If it so happens that this material is uber-strong and channels power; then you basically don't WANT to work with it. The most you may wish to do is tear some holes in the ceilings to give yourself some light, and then build inside the buildings. The old walls will make for excellent load bearing structural pieces that could form the core of your community, and then smaller wooden and stone structures would erupt around it in the form of regular housing. Their old roads would likely dictate the design of the vulture city built on the corpse.

One thing very similar to this is the city of Tal Verarr in Red Seas under Red Skies (the second book in the 'Gentleman Bastards' series by Scott Lynch). This place is built over Elderglass, left behind by the gods. Mostly because no-one can even work the stuff except maybe the Bondsmagi.

On the other hand, if this material is, like its creators, very vulnerable the magic of man; you probably want to remove it and replace it with mundane materials if you expect your city to be attacked by jealous neighbours. Or at least ensure that its parts are not visible to attack.

Thucydides has already covered some of the other main points, like people exploring the ruins. In terms of engineering challenges, I can't really say without knowing for sure about the materials.