Where they appear in groups, often in a circular, oval, henge or horseshoe formation, they are sometimes called megalithic monuments. These are sites of ancient religious ceremonies, sometimes containing burial chambers. The developments of radiocarbon dating and tree-ring calibration have added to our knowledge of their timing. In some archaeological sites, the remains of wooden henges can be found. Woodhenge was a henge and timber circle monument in the Stonehenge World Heritage Site in Wiltshire, England. It is 2 miles (3.2 km) north-east of Stonehenge.