"This stone circle is organised in a very complex way," he explained, as he showed us around the site. According to Carvalho, the stones follow a much more complicated equinoctial orientation than the one Stonehenge uses, which is based on the winter solstice. To find the equinox, the builders would have spent years observing the rising and setting of the Moon and the Sun, which suggests that the population was sedentary rather than nomadic, reflecting a monumental shift in human activity at that period.