or THERA, an island in the Aegean Sea belonging to Greece, the most southerly of the Cyclades, 13 miles S. of Nio, and about 60 N. of Crete. It is of the form of a horse-shoe or crescent, about 30 miles in circumference, and nowhere more than 3 miles across. This island was formerly united with Therasia, and formed a complete circle, having in the centre the deep crater of a submarine volcano, the rim of which may still be traced by the islands of Santorin, Therasia, and Aspronisi. The water in the inside is of great depth, though not, as was at one time supposed, unfathomable; and near the middle are three islets which have been thrown up by the volcano, two of them in ancient times, and the other, which is the largest, as late as 1707. The whole of the islands are of volcanic origin, except the southern part of Santorin, which is of limestone formation. In this portion, Mount Elias, the highest point, reaches an altitude of 1887 feet. The inner edge of the crescent formed by the island consists of rugged and steep precipices, from 500 to 1200 feet above the sea, and at the foot of these stand Epanomeria, Merovouni, and Thera, the chief towns; many of the houses nestling among the cliffs and accessible only by stairs cut in the rock. The other side of the island presents an agreeable contrast to these bare cliffs. It slopes gradually to the sea, and is entirely covered with vines, from among which numerous white villages rise. Barley, vetches, beans, figs, &c., are also raised; but the chief product of the island is its wine, which is of good quality, and the total value of which is upwards of L16,000 yearly. The whole annual produce of the island is about L24,000. Santorin contains thermal and mineral springs, but there is some scarcity of fresh water, and the inhabitants, though in other respects industrious, have done little to secure the small supplies they possess. Some ancient remains have been found, and there are numerous churches and convents belonging to the Greek and Roman Catholics. The only important circumstance connected with Santorin in ancient history is its having founded the celebrated colony of Cyrene, in Africa. Pop. (1848) about 14,380.