It comprises a group of 2,300-year-old structures, known as the Thirteen Towers, which are found in the Chankillo archaeological site, Peru.
The towers span the annual rising and setting arcs of the Sun, providing a solar calendar to mark special dates. The study is published in the journal Science.
Ã‚Â Clive Ruggles, professor of archaeoastronomy at Leicester University, UK, said: “These towers have been known to exist for a century or so. It seems extraordinary that nobody really recognised them for what they were for so long.
“I was gobsmacked when I saw them for the first time – the array of towers covers the entire solar arc.”