Gros Caillou, Glacial erratic in Croix-Rousse district, Lyon, France

Gros Caillou is a pale grey and beige quartzite boulder, weighing 24 tonnes, now set directly on the ground at the eastern end of Boulevard de la Croix-Rousse. Its rough, cracked surface has broad rounded faces and deep fissures, and it stands beside paved slabs with low vegetation around its base.

Workers struck an extremely hard rock in 1890 while cutting the inclined trench for the Croix-Paquet funicular, delaying the works until it could be extracted. On 12 April 1891 the block was set on a pedestal at the eastern end of Boulevard de la Croix-Rousse. Removed for the Espace Gros Caillou, it was laid directly on the ground when the esplanade was finished in 2008.

A local arts association bearing the stone's name was established in 1934 and recognized emerging writers and artists of the neighborhood. It played a role in promoting creative work during its active years.

The stone is easily reached from the Boulevard de la Croix-Rousse and is near the Croix-Rousse metro station, with several bus routes serving the area. It sits at an open spot on the boulevard where visitors can stop and look around without difficulty.

The block is a Triassic metaquartzite typical of Haute-Maurienne and Haute-Tarentaise, carried by the Rhône glacier during the Riss glaciation. A second, less documented account holds that the army dug galleries through the hill after the Croix-Rousse revolts and the stone was hauled out during that work.