One of the most famous ancient stone complexes is England’s Stonehenge, an impressive engineering and mathematical feat. Several groups of local inhabitants constructed this collection of large and small stones grouped in four concentric circles—two of which are created by paired upright stones bearing huge capstones—between 2950 and 1600 B.C.E. Based on how the stones line up with various astronomical events, historians believe the entire structure represents a huge (literally monumental) calendar. For example, various stones align with the Moon (the full moon’s extreme positions on the horizon are marked at Stonehenge) and with the Sun (including the summer solstice). It is also thought that the complex served as a place in which ancient rites and rituals were performed on significant days of the year. And it was all built without the help of computers.

The famous ancient structure of Stonehenge in England is now believed to have been designed to measure astronomical events as part of a religious tradition.