Before the water levels rose with the retreat of the ice sheets from the last Ice Age, Burry Holmes was once an inland hill overlooking a large plain. Nowadays, Burry Holmes is a tidal island and the Bristol Channel has submerged the plain.
It is thought that Mesolithic (Middle Stone Age) hunters used the hill as a seasonal hunting ground, to prepare hunting tools from flint, wood and bone, oversee the movement of herds on the plain and encourage deer into the area. Charcoal found on the site suggests that the hunting community may have burnt small parts the Severn Estuary woodland to make way for new plant growth, an attractive food source to the roaming red deer herds.
Over eighty small shards of flint (microliths) were discovered on the island between 1923 and 2001. These flint razors were probably embedded in rows onto the tip and shaft of wood, bone or antler, making effective spears for both fishing and hunting.
Later in history, the island was used by Iron Age people to build an impressive earthwork, then later still used as a hermitage/ecclesiastical site during Medieval times.