Santorini, is an island in the southern Aegean Sea, about 200 km southeast from Greece's mainland. It is the largest island of a small, circular archipelago which bears the same name and is the remnant of a volcanic caldera. It forms the southernmost member of the Cyclades group of islands, with an area of approximately 73 km2 and a 2011 census population of 15,550. The municipality of Santorini comprises the inhabited islands of Santorini and Therasia and the uninhabited islands of Nea Kameni, Palaia Kameni, Aspronisi, and Christiana. The total land area is 90.623 km2. Santorini is part of the Thira regional unit.Santorini is essentially what remains after an enormous volcanic explosion that destroyed the earliest settlements on a formerly single island, and created the current geological caldera. A giant central, rectangular lagoon, which measures about 12 by 7 km, is surrounded by 300 m high, steep cliffs on three sides. The main island slopes downward to the Aegean Sea. On the fourth side, the lagoon is separated from the sea by another much smaller island called Therasia; the lagoon is connected to the sea in two places, in the northwest and southwest. The depth of the caldera, at 400m, makes it possible for all but the largest ships to anchor anywhere in the protected bay; there is also a newly built marina at Vlychada, on the southwestern coast. The island's principal port is Athinias. The capital, Fira, clings to the top of the cliff looking down on the lagoon. The volcanic rocks present from the prior eruptions feature olivine and have a small presence of hornblende.It is the most active volcanic centre in the South Aegean Volcanic Arc, though what remains today is chiefly a water-filled caldera. The volcanic arc is approximately 500 km (310 mi) long and 20 to 40 km wide. The region first became volcanically active around 3–4 million years ago, though volcanism on Thera began around 2 million years ago with the extrusion of dacitic lavas from vents around the Akrotiri.The island is the site of one of the largest volcanic eruptions in recorded history: the Minoan eruption, which occurred some 3600 years ago at the height of the Minoan civilization. The eruption left a large caldera surrounded by volcanic ash deposits hundreds of metres deep and may have led indirectly to the collapse of the Minoan civilization on the island of Crete, 110 km to the south, through a gigantic tsunami. Another popular theory holds that the Thera eruption is the source of the legend of Atlantis.Excavations starting in 1967 at the site called Akrotiri under the late Professor Spyridon Marinatos have made Thera the best-known Minoan site outside of Crete, the homeland of the culture. The island was not known as Thera at this time. Only the southern tip of a large town has been uncovered, yet it has revealed complexes of multi-level buildings, streets, and squares with remains of walls standing as high as eight metres, all entombed in the solidified ash of the famous eruption of Thera. The site was not a palace-complex such as are found in Crete, but its excellent masonry and fine wall-paintings show that this was certainly no conglomeration of merchants' warehousing either. A loom-workshop suggests organized textile weaving for export. This Bronze Age civilization thrived between 3000 to 2000 BC, and reached its peak in the period 2000 to 1580 BC.
Some of the houses in Akrotiri are major structures, some amongst them three storeys high. Its streets, squares, and walls were preserved in the layers of ejecta, sometimes as tall as eight metres, and indicating this was a major town. In many houses stone staircases are still intact, and they contain huge ceramic storage jars, mills, and pottery. Noted archaeological remains found in Akrotiri are wall paintings or frescoes, which have kept their original colour well, as they were preserved under many metres of volcanic ash. The town also had a highly developed drainage system and, judging from the fine artwork, its citizens were clearly sophisticated and relatively wealthy people.Pipes with running water and water closets found at Akrotiri are the oldest such utilities discovered. The pipes run in twin systems, indicating that the Therans used both hot and cold water supplies; the origin of the hot water probably was geothermic, given the volcano's proximity. The dual pipe system, the advanced architecture, and the apparent layout of the Akrotiri find resemble Plato's description of the legendary lost city of Atlantis, further indicating the Minoans as the culture which primarily inspired the Atlantis legend.Fragmentary wall-paintings at Akrotiri lack the insistent religious or mythological content familiar in Classical Greek décor. Instead, the Minoan frescoes depict "Saffron-Gatherers", who offer their crocus-stamens to a seated lady, perhaps a goddess. Crocus has been discovered to have many medicinal values including the relief of menstrual pain. This has led many[who?] archaeologists to believe that the fresco of the saffron/crocus gatherers is a coming of age fresco dealing with female pubescence. In another house are two antelopes, painted with a kind of confident, flowing, decorative, calligraphic line, the famous fresco of a fisherman with his double strings of fish strung by their gills, and the flotilla of pleasure boats, accompanied by leaping dolphins, where ladies take their ease in the shade of light canopies, among other frescoes.The well preserved ruins of the ancient town often are compared to the spectacular ruins at Pompeii in Italy. The canopy covering the ruins collapsed in an accident in September 2005, killing one tourist and injuring seven more. The site was closed for almost seven years while a new canopy was built. The site was re-opened in April 2012.The oldest signs of human settlement are Late Neolithic, but ca. 2000–1650 BC Akrotiri developed into one of the Aegean's major Bronze Age ports, with recovered objects that had come, not just from Crete, but also from Anatolia, Cyprus, Syria, and Egypt as well as from the Dodecanese and the Greek mainland.