The “Druidical” sandstones of Wiltshire and Berkshire are so called. The early Christian Saxons used the word Saresyn as a synonym of pagan or heathen, and as these stones were popularly associated with Druid worship, they were called Saresyn or heathen stones. Robert Ricart says of Duke Rollo, “He was a Saresyn come out of Denmark into France.” Another derivation is the Phoenician sarsen (a rock), applied to any huge mass of stone that has been drawn from the quarry in its rude state.
These boulders are no more connected with the Druids than Stonehenge is (q.v.).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894