Les Trois Pierres dolmen, Dolmen in Saint-Nazaire, Loire-Atlantique, France

Les Trois Pierres is a trilithon dolmen: two gneiss orthostats, 1.94 m and 1.90 m high, support a 3.45 m by 1.80 m capstone estimated at 7.5 tonnes. A granulite menhir over 4 m long stands a few metres west, and two loose blocks lie near the north and south pillars. The stones stand on grass in a small square in central Saint-Nazaire.

The dolmen is first documented in a 1679 declaration by the seigneur de Marsaint, when the prior of Saint-Nazaire owed him a tribute placed half on a stone in the Marsaint courtyard and half on stones raised on the Île du Bois-Savary. Ogée's 1778 Dictionnaire de Bretagne gives a brief description, and Jean-Baptiste Huet a full one in 1801. Classified as a monument historique in 1889, it was long called dolmen du Prieuré, after the priory of Saint-Jean-Baptiste that once enclosed it.

The names record its setting: dolmen du Prieuré before the Revolution, when it stood in the walled domain of the priory of Saint-Jean-Baptiste, then dolmen de la Métairie or du Bois-Savary in the 19th century. Alain de Bizeul first wrote "dolmen des Trois Pierres". The square's other stones were set there later; the menhir was re-erected in 1928.

The dolmen and menhir stand in a small square in central Saint-Nazaire, at the corner of rue du Dolmen and rue du Menhir, about 400 m west of the port and 1 km southwest of the station. The stones are set on grass and bare earth beside a public street, so they can be seen at any time; the ground around them may be uneven or muddy after rain.

The dolmen is a trilithe: two uprights, 1.94 m and 1.90 m high, carry a 3.45 m table weighing about 7.5 tonnes, in gneiss. The menhir beside it, over 4 m long and 5 tonnes, lay flat for decades and was re-erected in May 1928 by Marcel Baudouin, who noted small cupules on its east face.