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. At 39.3 metres high, the hill is the tallest prehistoric man-made mound in Europe and one of the largest in the world; it is similar in volume to contemporary Egyptian pyramids. The site is in the care of English Heritage.