Traditionally, it is supposed to be the pillow stone said to have been used by the Biblical Jacob. According to one legend, it was the Coronation Stone of the early Dál Riata Gaels when they lived in Ireland, which they brought with them when settling Caledonia.
Another legend holds that the stone was actually the travelling altar used by St Columba in his missionary activities throughout what is now Scotland.
Certainly, since the time of Kenneth Mac Alpin, the first King of Scots, at around 847, Scottish monarchs were seated upon the stone during their coronation ceremony. At this time the stone was situated at Scone, a few miles north of Perth. (See BBC Excavation article below)
Another tradition holds that, in gratitude for Irish support at the battle of Bannockburn (1314), Robert the Bruce gave a portion of the stone to Cormac McCarthy, king of Munster. Installed at McCarthy's stronghold, Blarney Castle, it became the Blarney Stone.
A contemporary account by a Walter Hemingford, a canon of Guisborough Priory in Yorkshire says:
"Apud Monasterium de Scone positus eat lapis pergrandis in ecclesia Dei, juxta manum altare,
concavus quidam ad modum rotundae catherdeaie confectus, in quo future reges loco quasi coronatis."
(In the monastery of Scone, in the church of God, near to the high altar, is kept a large stone,
hollowed out/concave as a round chair, on which their kings were placed for their ordination,
according to custom.)