It is one of the greatest marvels of prehistoric Britain, the largest stone circle in Europe and a sacred meeting place for our ancestors which may even be aligned with the stars.

But a new archaeological survey at Avebury in Wiltshire suggests the Neolithic monument had far odder beginnings.

In fact, the huge circle started out life as a 100ft square, archaeologists now believe, after discovering a mysterious box-shaped enclosure of giant stones in the middle of the henge.

Henge monuments like Stonehenge and Avebury are always round. It is the first time such as square monument has ever been found. Earlier still, at around 3,500BC, experts found a simple rectangular wooden house occupied the site.