The Celtic hillfort of Otzenhausen is one of the biggest fortifications the Celts ever constructed. It was built by Gauls of the Treveri tribe, who lived in the region north of the fort. The first fortification was constructed in the 5th or 4th century BC, but the real heyday of construction dates to the 2nd and 1st century BC. For reasons yet unknown, the fort was abandoned shortly after this expansion.
The site is formed in the shape of a triangle with rounded ends. One rampart surrounds the whole fort. On the southern side, another similar embankment is built about 40 metres in front of the main one. The ends of this outer rampart approach the main one but do not touch it. Because the entrance of the main rampart is located on the western side, no significant purpose for the outer one has been determined. From west to east the fort extends 460 m, from north to south 647 m. The total length of the ramparts is 2500 metres and they contain 240,000 cubic metres of stone. Thousands of beams were attached to the ramparts which, as the diagram shows, probably presented a vertical stone wall to the exterior. Perhaps there was a second gate on the eastern side, but its existence is not yet proven.
In Roman time a small temple of 2.15 metres x 2.70 metres, dating from the 2nd or 3rd century A.D. was built of quartzite rubble stone and brick-shaped sandstone. When German tribes invaded the Roman territories in 4th century A.D, the fort was used again. During the Thirty Years War (1618–1648) the citizens of the surrounding villages again took refuge in the remains of the Celtic fort. Excavations took place in 1883 and from 1936 to 1939.References:
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.