Little is known about the Iron Age fort, with mysteries and theories around when it was built and why it was built on the low land rather than, as the name suggests, on a hill.
The two-week excavation dig, which is being led by archaeologists DigVentures and A Forgotten Landscape, a South Gloucestershire Council-funded landscape partnership, is hoping to turn back the hands of time to find out more about the purpose of the hillfort.