I know this is a joke/meme, but I sincerely think of the Roman Empire a surprising amount of times. I find myself obsessing over how Roman citizens were living just as complex lives as we are today, or about Marcus Aurelius’ life and philosophy, or about how the Republic fell and became a totalitarian state.
Once or twice a week, but only really because I do a lot of worldbuilding and part of that is taking inspiration from IRL civilisations.