Silbury Hill was built in the late Neolithic period, around 2400 BC. It is 30 metres high and 160 metres wide. Evidence suggests that it was not originally conceived as the monument seen today, but built up in stages over time. Approximately 500, 000 tons of material were used, mostly chalk quarried and cleared from surrounding terraces and ditches, involving an estimated 4 million man-hours of work. Its purpose and meaning are unknown. This photograph was taken from nearby Waden Hill.