It is possible that a prehistoric town in Brazil served as a site for ritual or ceremonial gatherings with a Pleiades star cluster as its inspiration. Following a survey of the pre-Hispanic stilt houses in northeastern Brazil's estuaries of the Maranho River, archaeologists came across the discovery. Formoso was one of the settlements examined, and it stood out due to its distinctive layout, elaborate pottery, size, and duration of use.

In the Journal of Archaeological Science: Reports, archaeologist Christopher Davis of McHenry County College in Illinois published the research with archaeologist Alexandre Guida Navarro of the Universidade Federal do Maranhão, Brazil, and said it looks to them "that the Formoso site may have been an elite ritual meeting site where sacred knowledge (like astronomy) was shared."

In Formoso, the crew investigated and found clusters of stilts that originally held larger structures than would be expected for residences, as well as unusually ornate ceramics with a fusion of local and foreign forms. 

Formoso, one of the several stilt villages examined, also demonstrated the longest period of continuous use; radiocarbon data showed that it was founded as early as 441CE and was sustained for around 500 years -- a marker of its significance.

Intriguingly, Navarro observed that the clusters of stilts that supported Formoso's buildings didn't follow the typical rectangular or circular patterns of Amazonian stilt towns or villages on land. The result was an odd design for Formoso. 

"We then considered other possible construction patterns (for defense, as fishing weirs, to reduce drag resistance of water currents or wind) and those scenarios didn’t fit either," Davis says.

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The two researchers didn't notice Formoso's striking resemblance to the Pleiades, a star cluster that was very important to Lower Amazonian tribes, until they started looking at constellation patterns.

"Finding a resemblance to a constellation was a bit of a surprise, but it was not surprising that the star cluster was the Pleiades," Davis says. "If any astronomy marker were used, it makes sense that it would have been the Pleiades."

According to Davis, the Pleiades' emergence in the Lower Amazon signaled the start of the dry season, a period during which residents repaired structural damage to their homes, restored and relocated fishing weirs and dams, and prepared their fields for the upcoming growing season.

It was also the time of year when some civilizations staged rites of passage ceremonies, and it was the most advantageous for individuals to travel great distances for business or to visit loved ones. The star cluster itself was interpreted as a beehive, a honeycomb, a valuable trade good, or a bundle of fire sticks for clearing the fields.

"It was very challenging to find ways to test whether or not the similarity to the Pleiades was just by chance," Davis says. "We had to learn and calculate several statistical correlation tests and probability to demonstrate that the resemblance is greater than 95% confidence—the standard level of confidence for scientific significance."

Together, the evidence from Formoso gives a suggestion that the village was a seasonal ceremonial or ritual center, where people from various locations gathered, and that its arrangement was a homage to the Pleiades as a changing seasons' herald.

Formoso's similarity to the Pleiades is now unmatched among the Amazonian stilt settlements, and it may continue to be so even with more study.