Since 1971, the Ministry of Education has operated a joint library service with the University of the South Pacific. Its library in Nuku'alofa has 9,000 volumes covering agriculture, small business management, adult education, and an important collection of Pacificana. The Ministry of Education library has 12,500 volumes. The Tonga College Museum's collection includes artifacts of Tonga's history. Notable monuments include the great trilithon known as the Ha'amanga and some 45 langis , great rectangular platforms of recessed tiers of coral limestone blocks that were erected as the tombs of medieval kings.