Mangaia (traditionally known as A'ua'u Enua, which means terraced) is the most southerly of the Cook Islands and the second largest, after Rarotonga. It is a roughly circular island, with an area of , from Rarotonga. Originally heavily populated, Mangaia's population has dropped by 75% in the last 50 years. Geography Originally known as A'ua'u or A'ua'u Enua ("terraced"), the island was named Mangaia (or Mangaianui-Neneva, "Mangaia monstrously-great") by Tamaeu, who came to the island from Aitutaki in 1775. Geologists estimate the island is at least 18 million years old. It rises 4750 m (15,600 ft) above the ocean floor and has a land area of 51.8 km2. Surrounded by a fringing coral reef, like many of the southern Cook Islands, it is surrounded by a high ring of cliffs of fossil coral 60 m (200 ft) high, known as the makatea. The inner rim of the makatea forms a steep cliff, surrounding swamps and a central volcanic plateau. The interior of the island is drained by underground channels passing through the makatea, leading to extensive networks of caves which have been used historically as refuges and for burials. The highest point is Rangi-motia, 169 m above sea level, near the centre of the island. Lake Tiriara is a body of fresh water in the south. History Excavation of the Tangatatau Rockshelter shows that Mangaia was first settled around 1000 CE. According to oral tradition, the island was not discovered, but emerged from the underworld of Avaiki already populated. It was later further settled from Rarotonga, Aitutaki, Atiu, Tonga and Tahiti. Adze heads and basalt tools show that trading contact was maintained with Rarotonga, Samoa, and Raiatea in the Society Islands. While sweet potato was likely grown as a crop earlier in the Pacific, the archaeological site at the Tangatatau Rockshelter is currently the earliest recorded location showing sweet potato cultivation in Polynesia. Initially settlement was focused on the coastal villages, but by the 16th century it had shifted inland and inter-island trade had virtually disappeared. Oral histories of this era are of chiefs competing for land and status. The island was first discovered by Europeans on 29 March 1777 with the arrival of Captain James Cook. It was visited by two more ships, one of which was possibly HMS Bounty, before the arrival of John Williams of the London Missionary Society in 1823. Williams was unable to land, but