Castra Praetoria

The rione takes its name from the Castra Praetoria, the camp of the Praetorian Guard. Italian Wikipedia's article on the Castra Praetoria dates its construction to 21-23 AD under Tiberius and gives its extent as 440 by 380 metres. Aurelian later absorbed its walls into his circuit, which is why the camp's northern and eastern sides survive as part of the city wall. Those two sides are what a visitor can actually see; the interior of the camp is a working barracks and is covered separately in this guide.