The UNESCO World Heritage Centre has included Odisha's Buddhist Diamond Triangle, comprising Lalitgiri, Udayagiri and Ratnagiri, in India's Tentative List. Together the sites record about 1,500 years of unbroken Buddhist history spanning Theravada, Mahayana and Vajrayana traditions. Lalitgiri, the oldest, dates to the 2nd-3rd century BCE and has a stupa containing relic caskets; Udayagiri thrived from the 1st to 13th century CE with large monasteries; and Ratnagiri was a leading Vajrayana centre often likened to Nalanda.