First a promise ~ I will not tell you every new and interesting fact I learn while making my way through some 3000 years of the everyday life of the human race. Promise.
Having said that, I have to tell you this. Human beings were not predisposed to build cities. The first ones were simply blocks of spaces with shared walls. There were neither streets nor doors. If you wanted to visit your friend who lived several spaces away, you climbed a ladder to the roof, crossed over the flat roofs, climbing up and down as necessary, and went in through a hole in the wall. Archeological affirmation of this fact comes from the city of Catal Huyuk in Turkey. According to the lecturer, Professor Robert Garland of Colgate University, some “Neolithic genius” (I Love that phrase) finally created the idea of streets and doors.
If I had thought about it all, I would have assumed that as caves had “doors” so would houses when they came along. And they did have openings - just not doors. There were no streets on which doors could open anyway. Fascinating.