The earliest traces of human settlement on the Sulzbach castle hill have been dated to the Late Hallstatt or Early La Tène culture. The medieval settlement was built first in the 8th century or early 9th century. The partially stone-made castle was built there in the 9th or 10th century. In 1003 the castle was moved to the Nordgaugrafen family by Henry II. The medieval castle was rebuilt from 1618 to the Renaissance style. Today the original tower from c. 1100 exists.
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.