The Tumulus of St. Michel is a megalithic grave mound, located east of Carnac. The 125m long, 60m wide and 10m high mound is the largest grave mound in continental Europe. The age of the monument, and the chronology of the construction of the central burial-chambers and outlying dolmen have been the subject of much speculation. Ancient samples were radiocarbon dated, but the results were too disparate to be significant. Recent excavations point to this large tumulus being constructed in several stages but in a rather short lapse of time, around the middle of the 5th millennium B.C. Today there is a chapel built on top of it.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.