Rome is also divided into differing types of non-administrative units. The historic centre is divided into 22 ''rioni'', all of which are located within the Aurelian Walls except Prati and Borgo. These originate from the 14 regions of Augustan Rome, which evolved in the Middle Ages into the medieval rioni. In the Renaissance, under Pope Sixtus V, they again reached fourteen, and their boundaries were finally defined under Pope Benedict XIV in 1743.