Plausible age for the ruins of a modern city skyline

Question

The setting is some indeterminate amount of time in the future. Humanity has had a rough recent history being rocked by wars, disease, and natural disasters and the current iteration of civilization is a shadow of what we know today. Most history has been lost and the knowledge of technology and science has been fractured and split. Heavy caliber machine guns are mounted on oxen drawn wooden carts. Coal fired mechanical forges create ceramic containers that people use to store the game they hunted for the winter. A fairly typical post apocalyptic environment.

One piece of the Old World remains however: stunningly enormous collections of spires that seem to pierce the sky. Clusters of them stand like giant artificial forests in what clearly used to be inhabited lands, but where no one has lived in existing memory. Some of these towering cities are by the coast, now standing in an ocean bay that rose up with the sea to consume them, some are inland at the bottoms of natural basins now overgrown with unending forests. The people of this new world almost worship the amazing beings that must have created these enormous structures and mourn that this era of their history is long since past.

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Question: How many years from today could this realistically be while keeping the cityscapes recognizable for what they were?

Assuming contemporary cities built using modern construction techniques and materials, how long could a place like Hong Kong, London, New York, Atlanta, or Tokyo be expected to be recognizable as cities? I'm specifically interested in how long the taller buildings might last, structures that would create a "ruined skyline" effect.

They don't need to be livable by any means, nor do the buildings need to be structurally sound (in fact collapses could be a good thing, plot wise). Think how today we look at the ruins of ancient Rome and the Parthenon in Athens: definitely ruins, but clearly recognizable for what they were and testaments to the skill of their builders.

I'm not looking for an exact number of course, but something at least in the order of magnitude. Could I say this is five hundred years in the future? A thousand? Or is only a single hundred years more realistic?

Answer 1

With the right location, 5000-10000 years

Some will fall over a lot sooner than this (100 years at worst, especially for the solid steel ones like empire state), but especially in dry, sheltered places, with no earthquakes, a city with skyscrapers will still have some skyscraper shapes visible for a long time.

Quoting from https://punctualabstract.com/2018/11/14/skyscraper/

So, will the skyscrapers of today still be around in the year 7,000 AD? According to Bill Baker, the man responsible for the structural integrity of the tallest skyscraper in the world, yes.

Skyscrapers constructed after the 1930s were made of concrete reinforced with steel, as opposed to just steel, which gave them the tensile strength of steel and the compressive strength of rock. They can resist both stretching and squeezing forces.

The earliest steel skyscrapers, like the Empire State Building, which date from the 1930s are least likely to remain standing in 7,000 years because they are constructed almost exclusively of steel, meaning they have exceptional tensile strength but are quite rigid and inflexible.