The Grey Cairns of Camster are two large Neolithic chambered cairns in the Highland region of Scotland. They are among the oldest buildings in Scotland, dating to about 5,000 years ago. The cairns demonstrate the complexity of Neolithic architecture, with central burial chambers accessed through narrow passages from the outside. They were excavated and restored by Historic Scotland in the late 20th century and are open to the public.
The cairns, which are considered to be examples of the Orkney-Cromarty type of chambered cairn, were constructed in the third or fourth millennium BC in a desolate stretch of boggy peat-covered moorland in the Flow Country of Caithness. They consist of two structures standing 180 m apart, known as Camster Round and Camster Long. A third cairn, located about 120 metres away from Camster Round, is not considered to be part of the grouping. Although the surrounding countryside is now inhospitable and sparsely inhabited, during the Stone Age it was fertile farming land and only became covered in peat during the Bronze Age.
Camster Long is a 60 m long cairn with 'horns' at each end. The two chambers appear to have originally been constructed within separate round cairns, which were only later incorporated into a single long cairn for unknown reasons.
Camster Round is, as the name suggests, a circular cairn; it measures 18 metres in diameter by 3.7 metres high. It is virtually intact with a high vaulted chamber at its centre, accessed from a passage 6 metres long and 0.8 metres high at the east-south-east side of the cairn. The passage appears to have been deliberately put out of use by blocking it up with stones piled up to the height of its roof.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.