Durrington Walls is a multi-phased Neolithic site (more than 4.500 years old) located 3.2 km north-east of Stonehenge, next to the river Avon. At 500 metres (1,600 ft) in diameter, it is the largest henge in Britain. In 2015 an announcement was made by The Stonehenge Hidden Landscapes Project that a geophysical survey showed evidence of another monument consisting of up to 90 standing stones buried under Durrington Walls. In August 2016 a joint project excavation (Stonehenge Riverside Project and LBI ArchPro) revealed that there are no buried standing stones at Durrington Walls. The ground-penetrating-radar results had actually revealed a circle of enormous post-holes, not buried stones, beneath the henge bank which had been later filled with chalk rubble.