The Ingá Stone

A 46-metre wall of carvings in a Brazilian river, still unread

In the middle of the Ingá River in Paraíba, 96 kilometres from João Pessoa, a wall of gneiss 46 metres long and 3.8 metres high is covered in carvings nobody has read. It is also called Itacoatiara do Ingá, from the Tupi word for stone. Among the glyphs are figures that look like animals, fruits and people, and signs that seem to show the sky, among them Orion and the Milky Way. Scholars believe it was made by the native people who lived in the area until the 18th century. From 1976 the Spanish engineer Francisco Pavía Alemany studied it mathematically and argued that a row of carved hollows and a gnomon formed a solar calendar, catching the first rays of each day, and that clusters of signs on the rock are constellations; in 2006 the Egyptologist and archaeoastronomer José Lull published the case alongside studies from four continents. What the carvings say is still undeciphered, and the rock is under constant threat from scavengers and vandals.