Trilith of Rio Grande do Sul

29.5000°S, 51.0000°W.

The Trilith of Rio Grande do Sul in southern Brazil — a megalithic stone arrangement of three large dressed boulders forming a trilithon (two upright stones supporting a horizontal lintel) of disputed date and attribution. Construction date is recorded only as prehistoric, with no secure radiocarbon or stratigraphic evidence published in the peer-reviewed archaeological literature. The structure consists of two granite uprights approximately 3 metres tall supporting a lintel block weighing approximately 8 tonnes; the three stones are dressed and fitted to a degree unusual for southern Brazilian indigenous traditions. The Trilith has been the subject of competing interpretations: a deliberately constructed megalithic monument predating Portuguese contact, a natural erosional feature later modified, or a colonial-period folly. No conclusive excavation has been published. The structure is one of several disputed pre-Columbian megalithic claims along the southern Brazilian and Uruguayan coasts.

A trilithon in southern Brazil whose date, builders, and purpose have all been argued without resolution since the structure was first reported in nineteenth-century European travel literature.