Holmbury Hill is the site of an Iron Agehillfort close to the village of Holmbury St. Mary in Surrey, England. Excavation of the site in 1929 by S.E. Winbolt indicated that it dated to the 1st Century AD and may have been constructed by Belgic tribes of Celts who were settling this part of Britain in the period prior to the Roman invasion of Britain. The hillfort was defended by double ramparts to the west and north with escarpments on the eastern and southern slopes. The outer ditches were originally about three metres deep and six metres wide. The inner ditches were considerably larger, some four metres deep and nine metres wide.
At 857 feet, Holmbury Hill is the fourth highest point in the county of Surrey. It is two miles west of Leith Hill, the highest point in Surrey at 965 feet.