To be fair, industrial-level civilization (engines, mass production, etc) doesn't actually require large, reinforced concrete structures[0]. That said, the ans

To be fair, industrial-level civilization (engines, mass production, etc) doesn't actually require large, reinforced concrete structures[0]. That said, the answer to TFA's question is "almost certainly yes, unless they deliberately tried to conceal geological evidence of their existence, and probably even then". 0: nor vice versa, technically, though the logistics of using pre-industrial steel as building material would be prohibitive. see https://news.ycombinator.com/item?id=24591216 https://news.ycombinator.com/item?id=24591216