SILBURY HILL – WILTSHIRE (U.K.)
Silbury Hill is the tallest prehistoric man-made mound in Europe and one of the largest in the world; similar in size to some of the smaller Egyptian pyramids of the Giza Necropolis. Silbury Hill is part of the complex of Neolithic monuments around Avebury, which includes the Avebury Ring and West Kennet Long Barrow, in the English county of Wiltshire UK.
It was built in three stages and over a period of probably about 30 or 40 years. The first began in 2600 BCE which makes it contemporary with the megaliths at Avebury and also with the pyramids in Egypt. The mound consists of thousands of chalk bricks forming walls enclosing terraced infill at three levels. The mound was then graded with chalk to give an angle. Quartz crystals found in the surface soil were probably placed to reflect the moonlight and would have created quite a spectacular beacon for miles around.
The last phase comprised the building of six concentric steps or terraces of chalk which were then covered with chalk rubble, flints, gravel, and finally soil to form a cone-shaped mound the hill itself contains about 324,000 cubic metres of chalk and soil, is encircled by a ditch some 5 metres deep and 20 metres wide from which some 170,000 cubic metres of soil and chalk were excavated.
Composed mainly of chalk and clay excavated from the surrounding area, the mound stands 40 metres (131 ft) high and covers about 5 acres. The hill was constructed in several stages between 2400–2300 BC and displays immense technical skill and prolonged control over labour and resources. Archaeologists calculate that it took 18 million man-hours, equivalent to 500 men working for 15 years to deposit and shape 248,000 cubic metres (324,000 cu yd.) of earth and fill.
The initial structures at the base of the hill were perfectly circular: surveying reveals that the centre of the flat top and the centre of the cone that describes the hill lie within a metre of one another. There are indications that the top originally had a rounded profile, but this was flattened in the medieval period to provide a base for a building, perhaps with a defensive purpose.
TSilbury Hill is a massive artificial mound with a flattened top which is around 98 feet across. It is approximately 131 feet (40 m.) high, with a base circumference of 548 feet (167m. It is composed of over 324.000 cubic yards (248,000 cubic m.) of chalk and earth and covers over 5 acres (2 ha).
(Source : http://www.philipcoppens.com/nap_art3.html)