Helen Mark visits the Beaghmore Stone Circles in Co Tyrone. It's a mysterious, mystical site with seven circles, 10 rows of stones and 12 cairns, all seemingly carefully aligned. They were found by turf cutters in the 1930s, excavated in the 1960s and carbon dated back to the early Bronze Age. There are many theories about what they were used for - perhaps a burial site, a place for harvest ceremonies, or some sort of lunar or solar calendar
