Where menhirs (standing stone, orthostat, or lith) appear in groups, often in a circular, oval, henge or horseshoe formation, they are sometimes called megalithic monuments. These are sites of ancient religious ceremonies, sometimes containing burial chambers. Sillustani is a pre-Incan burial ground on the shores of Lake Umayo near Puno in Peru. The tombs, which are built above ground in tower-like structures called chullpas, are the vestiges of the Colla people, Aymara who were conquered by the Inca in the 15th century. Drawing taken from page 432 of "Peru: incidents of ravel and exploration in the Land of the Incas" by Ephraim George Squier, 1877.