Silbury Hill
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Silbury Hill is one of the largest prehistoric human-made mounds in the world. It's believed to have been built between 2470 and 2350 BC. Its original purpose is unknown. The mound is composed mainly of chalk and clay and it stands about 30 metres high. The mound we see today was not constructed in a single campaign, but enlarged over several generations. The mound was excavated in 1776 by Edward Drax, who directed a group of miners to dig a vertical shaft from the summit to the centre of the mound. Edward Drax expected to find a central burial chamber, but he didn't find anything. The mound was excavated again in 1849. This time, a horizontal tunnel was dug into the mound. Again, no central burial chamber was found. Between 1968 and 1970, another tunnel was excavated. This investigation led to the conclusion that Silbury Hill had three different phases of construction. The tunnels were never backfilled which contributed to the opening of a crater on the summit and the collapsi