Near an oasis in the coastal desert of Peru lies one of the strangest structures in the Americas. The structure is a fort built at the top of a hill with a line of 13 towers constructed to its south.
The fort is odd from a military point of view because it would have been almost impossible to defend: it has numerous entrances and no source of water inside. Then there are the towers, which are several hundred metres from the hilltop fort, lie in a straight line and serve no discernible defensive role.
So in 2007, archaeologists put forward a new interpretation. They suggested the site may have been a place of worship and a solar observatory, like Stonehenge, rather than a fort.
Their main evidence was that the towers line up with the sunrise on important dates such as summer and winter solstice.
Today, Amelia Sparavigna at the Politecnico di Torino in Italy adds some evidence using a program developed for calculating the position of the sun in the sky to determine how much sunlight should fall on solar panels.
She uses the program to show that the first tower lines up with sunrise on 21 June and the last tower lines up with the sunrise on 21 December.
She also shows the shadows the towers throw are useful too. Since the site is tropical, the shadows point north for half the year and south for the other half. What’s more, when there are no shadows the sun is at its zenith.
She points out that this would have been important information for a farming community, which would need to know when to plant seasonal crops.