Parque Arqueológico do Solstício (Calçoene, 'Amazonian Stonehenge')

The Parque Arqueológico do Solstício, or Solstice Archaeological Park, is known in academic sources as AP-CA-18. It lies in Amapá state, Brazil, near the city of Calçoene, on a hilltop at the bank of the Rego Grande river. It contains a megalithic stone circle, colloquially called the Amazon Stonehenge, which gives the site its nickname.

The circle consists of 127 blocks of granite, each up to 4 meters tall, standing upright in a ring over 30 meters in diameter. Apart from one stone with a circular hole carved into it, the granite blocks appear irregularly shaped. Whether that irregularity reflects primitive mining technology or holds clues to possible uses has not been determined. The origin of the granite has yet to be studied, and archaeologists are not yet sure whether the blocks were brought from elsewhere.

The first reports of the Rego Grande site come from the naturalist Emilio Goeldi in the late 19th century, and locals have called it Tropical Stonehenge for some time. In 2005 archaeologists began excavating after a geologist reported it during a socioeconomic study. The stones have not been dated, but carbon-dating of pottery sherds places the site at 500 – 2000 years old.

Archaeologists believe the site was built by indigenous peoples for astronomical, ceremonial or burial purposes, and probably a combination. On the winter solstice of December 21, the shadow of one block disappears when the sun is directly above it. During the winter solstice the sun also shines through the circular hole onto another rock for an extended time. These alignments lead archaeologists to think the site was once a type of astronomical observatory, although its function remains unknown.

Excavations found two large pits, both approximately 1.5 – 2 meters deep and covered by large stone slabs. One held three intact urns in a triangular formation, the other more urns and a few lids, together with pottery shards, red clay and ash from human remains. This suggests the pits were burial sites or held select remains of special significance. Bowls, lids and urns were made in the shapes of animals and human-like figurines. Other megalithic sites in Brazil follow the curves of the Rego Grande river, which suggests the site may have been ceremonial and shared among different indigenous communities. Most scientists agree it points to a pre-Cabraline society much more complex than previously thought.

The first reports of the Rego Grande site are from naturalist Emilio Goeldi in the late 19th century. Locals have called the site "Tropical Stonehenge" for some time. In 2005, archaeologists began excavation of the site after it was reported by a geologist during a socioeconomic study.