The late 15th century Baia Castle was built by the over ancient Roman ruins thought to be the summer residence of Julius Caesar. On the 29th September 1538 the great eruption, with devastating effects for all the Phlegraean Fieldsi, caused serious damage to the Castle of Baia too. The castle was restored and enlarged by the viceroy don Pedro Alvarez de Toledo.
Today, this cliffside Aragonese castle with sea views is home to the Archaeological Museum of Campi Flegrei.
The city walls of Avila were built in the 11th century to protect the citizens from the Moors. They have been well maintained throughout the centuries and are now a major tourist attraction as well as a UNESCO World Heritage Site. Visitors can walk around about half of the length of the walls.
The layout of the city is an even quadrilateral with a perimeter of 2,516 m. Its walls, which consist in part of stones already used in earlier constructions, have an average thickness of 3 m. Access to the city is afforded by nine gates of different periods; twin 20 m high towers, linked by a semi-circular arch, flank the oldest ones, Puerta de San Vicente and Puerta del Alcázar.