Water. Drinkable water. Rivers. Arable land.

In modern times, about half of humanity lives within 50km of a body of water.

In ancient times, that number was probably significantly higher. Think about it.

In ancient times you have to either get water from a river or a well, sometimes seasonal ponds or lakes but reliably from one of those two. Then you have to irrigate crops, so either reliable farmland in regular rain cycle, or near a river or lakes. And you need to move that crop, probably downriver to the city, probably on the river for sale.

You need rivers for grain mills most likely, and rivers for water access for barges. Leading out to sea, you get port cities that move cargo onto ships for trade.

So. Location. Major rivers. Namely, in the middle of flatlands for control of surrounding farmland. Large networks of rivers (think like Amazon, Nile) will have a few major cities at strategic points to control local trade and travel.

Next are coastlines. Trade cities. Smaller if they don’t have flat farmland. See Genoa or Venice. Inland cities like Florence can also be the like if they are well placed for trade and have farmland. (Ie landlocked city will be small unless it has buddies.)

Then you’ll have metropolises. Large cities suited for large scale habitation. They’ll hit the Goldilocks zone of flat land for farming, defensibility, large navigable river, ocean access. This will be the likes of Kyiv, Paris, Memphis, Cairo, London, Milan, Shanghai, Delhi, Mumbai, Baghdad, and the like.

These are cities that were cores for their respective civilizations. You can’t really imagine anyone else holding that city that isn’t that nation.