[SunkenCiv]

This one is one of the few which has a definite start date, assuming that much of it wasn't already in existence when the order was given (6000 apartments is a remarkable about of work getting done by a fairly small number of people with medieval infrastructure support (the food, the water) in the middle of nowhere. Many of these structures are found in Anatolia, and Robert Schoch (among others) has suggested that they continued to be expanded and extended, but that the original excavations go back to the Neolithic.

[Openurmind]

I believe it, That's what I understand also, some were used for a long term. That's what makes me wonder if there was some sort of climatic or solar event that forced them underground for survival reasons in the earliest examples and then they just continued to utilize these after. I'll have to dig into all my Paleoclimatology references and see if there might have been a connection. You have me curious now. :) Have you checked out the Longyou Grotto's yet? Way too cool and they have no clue who made them or how old they really are. Just incredible stonework and craftsmanship! https://interestingengineering.com/ancient-man-made-longyou-caves-surrounded-mystery