Bilgroix gallery grave, Prehistoric burial structure in Arzon, France.

Bilgroix gallery grave is a prehistoric burial chamber in Arzon made of stone walls supporting large capstones. A passage leads through the structure to the burial chamber, with the western end sealed by an upright stone slab and the floor lined with paving stones.

The structure was built during the Neolithic period around 2900 to 2500 BC as a megalithic burial site in Brittany. Archaeological finds including pottery vessels and flint tools from the region confirm its use as a place for the dead.

The gallery grave shows how Neolithic communities honored their dead and organized burial rituals in their society. The way the stones are arranged reveals what people valued and knew about construction during that era.

The monument stands on the north-west flank of the Pointe de Bilgroix summit, at 14 m altitude, near Port Navalo at the western tip of the Rhuys peninsula. The cairn was levelled in 1912, so its present height is lower than the 3 to 4 m recorded in 1866. Only one covering slab, 3.30 m by 2.80 m, remains in place above the passage.

The monument was long called a dolmen, but it has no separate chamber: it is a single passage 14 m long, 1.25 m wide at first and widening to 1.80 m, ending at an upright slab 1.60 m high. A small annex grave south of the cairn held no finds, and a dry-stone structure shaped like an S lies to its east.