Under the Roman Empire, the rich people lived in villas. Large windows allowed residents to look out on urban life — and for urban life to look in. More often than not, the villa’s entrances opened directly onto city streets. As the power of the Roman Empire began to wane, the cities became less safe. Villa walls got thicker and their windows became smaller. Some moved into military fortifications that the empire had abandoned.

Out of these changes, the medieval castle gradually emerged as the new dwelling of choice for the well-to-do. Usually elevated above the homes of commoners, the castle’s walls, moats, and drawbridges could easily be mistaken for a show of strength. But in truth, they were a symbol of the decline of pax romana, a testament to the absence of a centralized source of protection and power. In this new world, every man was on his own.