We here at the _floss go positively mental when archaeologists find cool new things, and these 13 towers in Peru, built 2,300 years ago and believed to have been used to measure the motion of the sun across the sky, is one of the coolest in recent memory. The towers, at a site called Chankillo, were discovered about 100 years ago, but it wasn’t until this week that archaeoastronomists figured out what they were for. These pictures are worth 1,000 words, but essentially the towers functioned as an ancient calendar. Professor Clive Ruggles of the U of Leicester explains: “On the summer solstice, which is in December in Peru, you would see the Sun just to the right of the right-most tower; for the winter solstice, in June, you would see the Sun rise to the left of the left-most tower; and in-between, the Sun would move up and down the horizon.” What we don’t know, however, is much about the people who built this impressive structure; the famous sun-worshiping Incas didn’t emerge until hundreds of years later. Who were these ancient astronomers?