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Silbury Hill is a prehistoric artificial chalk mound near Avebury in the English county of Wiltshire. It is part of the Stonehenge, Avebury and Associated Sites UNESCO World Heritage Site, and lies at . At high, Silbury Hill – which is part of the complex of Neolithic monuments around Avebury, which includes the Avebury Ring and West Kennet Long Barrow – is the tallest prehistoric man-made mound in Europe〔Atkinson 1967.〕 and one of the largest in the world; it is similar in size to some of the smaller Egyptian pyramids of the Giza Necropolis.〔Malone (1989), p. 95.〕 Its original purpose is still highly debated. Several other important Neolithic monuments in Wiltshire in the care of English Heritage, including the large henges at Marden and Stonehenge, may be culturally or functionally related to Avebury and Silbury. ==Structure== Composed mainly of chalk and clay excavated from the surrounding area, the mound stands high〔The measurement is taken from the present ground level at the top of silt that has accumulated in the trench surrounding the tumulus, to a depth of nine meters (Atkinson 1974:127).〕 and covers about . It is a display of immense technical skill and prolonged control over labour and resources. Archaeologists calculate that Silbury Hill was built about 4,750 years ago and that it took 18 million man-hours, or 500 men working for 15 years (Atkinson 1974:128) to deposit and shape of earth and fill on top of a natural hill. Euan W. Mackie asserts that no simple late Neolithic tribal structure as usually imagined could have sustained this and similar projects, and envisages an authoritarian theocratic power elite with broad-ranging control across southern Britain.〔Mackie, ''Science and Society in Prehistoric Britain'' (New York: St. Martin's Press) 1977.〕 The base of the hill is circular and in diameter. The summit is flat-topped and in diameter. A smaller mound was constructed first, and in a later phase much enlarged. 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.〔Atkinson 1974 p. 128〕 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. The first phase, carbon-dated to 2400 BC ±100 years, consisted of a gravel core with a revetting kerb of stakes and sarsen boulders. Alternate layers of chalk rubble and earth were placed on top of this: the second phase involved heaping further chalk on top of the core, using material excavated from an encircling ditch. At some stage during this process, the ditch was backfilled and work was concentrated on increasing the size of the mound to its final height, using material from elsewhere. The step surrounding the summit dates from this phase of construction, either as a precaution against slippage, or as the remnants of a spiral path ascending from the base, used during construction to raise materials and later as a processional route.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Silbury Hill」の詳細全文を読む スポンサード リンク
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