Octogone de Montmorillon, Romanesque chapel in Montmorillon, France

The Octogone de Montmorillon is a 12th-century Romanesque cemetery chapel with an octagonal body of pale ashlar blocks and a steep dark roof topped by a small lantern. It has two levels, having been built over an ossuary. Its front arch holds a red double door, with a niche of five standing figures above and carved corbels and modillions around the stonework.

The chapel belonged to the Maison-Dieu of Montmorillon, founded around 1080-1085. Its roof was ruined by 1584 and rebuilt between 1611 and 1639 with a pyramidal timber frame, a slate-and-lead dome bell tower and a lantern, apparently destroyed by 1724. It was listed as a monument historique in 1840 and restored in 1997-1999 to its 17th-century appearance, with the bell tower rebuilt as a campanile-like lantern.

The carved stone surfaces inside display many figures including animals and human forms, along with scenes from religious texts. These detailed works show the skill of medieval craftsmen who created them.

The building sits on Rue des Augustins and underwent major restoration work between 1997 and 1999. These repairs focused on preserving and restoring its original architectural features.

The octagonal plan may draw on the octagonal Dome of the Rock in Jerusalem (681) or Charlemagne's palatine chapel at Aachen (792). Within the Maison-Dieu enclosure there were two octagons: the second, smaller one is considered a warming room.