Originally, there were six gates in the surrounding wall which were reduced to three in the 16th century. The only one remaining today is the Porta Napoletana (Neapolitan Gateway).
It was built in 1511 -1519 by the Lombard masons and still stands today almost intact on the Appian Way, facing south. The imposing construction has a central body with two strong, semi circular side turrets. The sign carved on one of these doorjambs “Si paga gabella” (“duty tax”) explains the purpose of the trade barrier of the fortified entrance during the Renaissance period.
It was restructured and fortified in 1700 and restored in 1991.