Stonehenge is a prehistoric monument located in Wiltshire, England composed of earthworks and large standing stones erected around 2500 BC. It consists of large stone blocks arranged in concentric circles, with an exterior circle of large stones and an interior circle of smaller bluestones. Within is a horseshoe structure of sandstone and a central altar slab. The origin and purpose of Stonehenge remains mysterious as the culture that built it left no written records, but it was likely used for ceremonies and sacrifices.