The cap-stone of the tumulus has been determined to be a small part of a larger stone, other parts of which were used as capstones for the nearby Table des Marchands and the Gavr'inis passage mound.

Chronology - Archaeology of the site indicates an original construction  date from the fifth millennium (1), (2). The original 'cairn' was extended in both directions into its final shape and a pavement surrounded the stepped tumulus. The capstone dates the final construction phase for the tumulus at approximately 3,300 BC along with the aforesaid structures.

Whittle says of this: 'In front of the south facade of the primary phase of the long cairn of Er Grah, close to where the menhir Brise originally stood...a pair of domesticated cattle were found in a pit (Tresset and Vigne, forthcoming; Anne Tresset, pers. comm.; cf. Tresset 2000). Radiocarbon determinations suggest a date in the late sixth and early fifth millennium BC...' (1)

(Map of Location)

The Capstone.