A stone library in the riverbed
In the agreste region of Paraíba state, the Ingá River flows around a massive rock formation of gneiss. Known as the Pedra do Ingá, or Itacoatiara do Ingá, this stone is not a blank canvas. The surface has more than 400 carved petroglyphs, creating one of Brazil's most significant archaeological sites. The main vertical wall is 46 meters long and stands up to 3.8 meters high. The entire rock art panel covers an area of about 250 square meters.
The age of the carvings is uncertain, with some estimates suggesting they are at least 6,000 years old. This dating is difficult because the stone sits in a riverbed and is subject to periodic flooding, which can contaminate sediments used for analysis. The symbols are varied. They include representations of animals, fruits, and human-like figures, alongside many abstract geometric shapes. The technique used was not simple etching; the creators pecked at the hard gneiss and then polished the grooves, a laborious process. Microscopic analysis also detected faint reddish residues in some carvings, suggesting they might have once been colored with pigment.
Brazil's celestial map
The meaning of the Ingá symbols is the subject of intense debate, with no single theory achieving a scholarly consensus. The most prominent scientific hypothesis frames the site as an ancient astronomical observatory. In 1976, Spanish engineer Francisco Pavía Alemany began a mathematical study of the site. He identified a group of bowl-shaped depressions, or "bowls," and other markings on the main vertical wall that he proposed functioned as a solar calendar. A gnomon, a type of primitive sundial post, could have been used to project the sun's shadow onto the panel, tracking the days.
Further research by Pavía and others identified engravings that appear to map celestial bodies. Some groupings of symbols strongly resemble constellations, most notably Orion and the Milky Way. The combination of the solar calendar and the star maps gives the site its archaeoastronomical importance. Other theories are more speculative. Researcher Gabriele D'Annunzio Baraldi noted similarities between some Ingá symbols and ancient scripts from different parts of the world, including Hittite, Phoenician, and Nordic runes. This has led to fringe ideas about trans-oceanic contact or lost civilizations, but these lack empirical evidence. Mainstream archaeology generally attributes the work to the indigenous peoples who inhabited the region until the 18th century.