Editing Silbury Hill (section)

==Structure==
{{Mapframe|type=point|frame=yes|zoom=12|frame-width=250|text=Interactive map of Silbury Hill}}

Composed mainly of chalk and clay excavated from the surrounding area, the mound stands {{convert|39.3|m|ft|0}} high{{efn|
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 metres.{{sfnp|Atkinson|1974|p=127}}
}} and covers about {{convert|2|ha|acre|0|abbr=}}. The hill was constructed in several stages between {{circa|{{nobr|2400~2300 {{sc|BC}} }}}}<ref name=Jones>{{cite book |url=https://books.google.com/books?id=h3q2Y3GVpAEC&pg=PA181 |page=181 |title=Prehistoric Materialities: Becoming material in prehistoric Britain and Ireland
|last = Meirion Jones |first = Andrew |year=2012 |publisher = [[Oxford University Press]] |isbn = 978-0-1995-5642-7 }}</ref> and displays immense technical skill and prolonged control over labour and resources. Archaeologists calculate that it took 18&nbsp;million man-hours, equivalent to 500&nbsp;men working for 15&nbsp;years<ref name=Atkinson-1974-128>{{harvp|Atkinson|1974|p=128}}</ref> to deposit and shape {{convert|248000|m3|yd3}} of earth and fill. [[Euan 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.<ref>Mackie, ''Science and Society in Prehistoric Britain'' (New York: St. Martin's Press) 1977.</ref>

The base of the hill is circular and {{convert|167|m|ft}} in diameter. The summit is flat-topped and {{convert|30|m|ft}} 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.<ref name=Atkinson-1974-128/> 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.<ref name=eh/>

The first clear evidence of construction, dated to around {{nobr|2400 {{sc|BCE}},}}<ref name=NMR>
{{cite report
 |title=Silbury Hill
 |year=2007
 |series=National Monument Record
 |publisher=[[English Heritage]]
 |url=http://pastscape.english-heritage.org.uk/hob.aspx?hob_id=220743
 |url-status=dead |access-date=24 June 2009
 |archive-url=http://webarchive.nationalarchives.gov.uk/20100910153854/http://pastscape.english%2Dheritage.org.uk/hob.aspx?hob_id%3D220743
 |archive-date=10 September 2010
}}
</ref> consisted of a gravel core with a revetting [[Megalithic architectural elements#Kerb or peristalith|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 a series of surrounding ditches which were progressively refilled then recut several metres further out.<ref name=Jones/> The step surrounding the summit dates from this phase of construction, either as a precaution against slippage,<ref>
{{cite book
 |last = Darvill |first = Timothy
 |year = 1996
 |title = Prehistoric Britain |edition=2
 |publisher = Routledge
 |location = London, UK
 |isbn = 0-415-15135-X
 |page = [https://archive.org/details/prehistoricbrita00darv/page/n93 93]
 |url = https://archive.org/details/prehistoricbrita00darv
 |url-access = limited  |via = [[Internet Archive]] (archive.org) 
}}
</ref> or as the remnants of a spiral path ascending from the base, used to raise materials during construction, and later as a processional route.<ref name=BA70/><ref name=NMR/>

Silbury Hill was originally entirely white since it had a chalk (limestone) exterior, and the surrounding ditch may have been regularly filled with water from underground springs.<ref>
{{cite web
 |title=Silbury Hill
 |series=Avebury
 |website=Bradshaw Foundation
 |url=https://www.bradshawfoundation.com/avebury/silbury_hill/index.php
}}
</ref>