The Mura di Ostuni, or the walls of Ostuni, are defensive structures rebuilt by the Aragonese to protect the historic center of the city. These whitewashed walls have cylindrical towers and used to have four gates; now only Porta Nova and Porta San Demetrio remain. They offer a glimpse into Ostuni's history, and if you walk along them, you can also enjoy the beautiful views surrounding this hilltop city.