Tumiac tumulus, Megalithic tumulus in Arzon, France

Tumiac tumulus is a conical mound about 15 m high and 55 m across at its base, built entirely of clay and earth over a stone cairn. At its foot, four upright stones frame a rectangular entrance with a flat lintel, leading into a dark passage. The cairn holds a chamber 2.40 m square, roofed by a single quartz slab and closed on three sides by engraved orthostats. A crater at the summit marks the 1853 excavation shaft.

The Tumiac tumulus is one of the large "Carnac-type" Neolithic mounds, built around 4000 BC as an elite burial monument, comparable to the Tumulus Saint-Michel at Carnac and Mané-er-Hroek at Locmariaquer. It was first explored in 1853 by Louis Galles and Dr Alfred Fouquet of the Société polymathique du Morbihan, after a trench had been opened in its south side. Zacharie Le Rouzic excavated again in 1934, uncovering a second, smaller dry-stone cist beside the main chamber. The finds, including 32 polished axes and three callaïs necklaces of 237 beads, are kept at the archaeological museum in Vannes.

Locals call it Butte de César, from a tradition that Julius Caesar watched the naval battle against the Veneti from here in 56 BC. The mound was raised around 4000 BC, and the crater still visible on top comes from the vertical shaft dug during the 1853 exploration.

The interior is closed to the public because the mound is unstable, so the monument is seen only from outside; the crater at the top is the vertical hole dug for the 1853 exploration. The site lies in Arzon on the Rhuys peninsula, south of the Gulf of Morbihan.

The 1853 diggers entered through a trench cut into the south side and found a "grotto"; the crater still visible on top is the vertical shaft sunk for that exploration. The finds — 32 axes, three callaïs necklaces of 237 beads, a worked ox horn — are kept at the archaeological museum in Vannes.