Stonehenge is just one of almost a hundred vast circular earthworks built in the British Isles over four thousand years ago. Known as henges, they remain one of the mysteries of prehistoric Britain. Unlike stone circles, which are their counterparts in the west, henges have generally been ignored. With their overgrown banks and weathered ditches they attract few visitors. Yet discoveries have revealed fascinating glimpses of the beliefs of their builders. Excavations have unearthed grim evidence of forgotten rituals: a child's sacrifice at Woodhenge; a human burial at the centre of Arbor Low; a woman's skull at the entrance to Gorsey Bigbury; winter moonlight at Stonehenge.Such things hint at the power and importance that these huge enclosures once had. The effort needed to raise these spacious rings of earth or chalk, the careful planning of their entrances, the settings of stone or timber inside them and the avenues leading uphill from nearby rivers all make henges among the most exciting and intriguing of the ancient monuments of the British Isles.