Although many visitors now come to Santorin by air, the approach by sea, entering the crater from the northwest, is an experience which should not be missed. After passing the gentle green slopes on the outside of the island the boat enters the huge central basin, almost totally enclosed by sheer rock walls.
Santorini or Thíra (Thera, the Wild Island; Italian Santorino or Santorini, after the island's patron saint, St Irene), the most southerly of the larger Cyclades, and the smaller islands of Thirasía (9 sq. km/3.25 sq. mi; 295m/970ft) and Aspronísi (2 sq. km/.75 sq. mi; 71m/233ft) are remnants of a volcanic crater which has been engulfed by the sea. The rim of the caldera emerges from the sea in a ring, open to the northwest and southwest, enclosing a basin up to 400m/1,300ft deep, in the center of which are the two Kaiméni islands, the peaks of a later volcano which came into being in historical times. Hot springs and emissions of gas bear witness to continuing volcanic activity.
The dense volcanic deposits lie on top of a massif of argillaceous schists and graywacke overlaid by semi-crystalline limestones. The highest point on the island is Mt Profítis Ilías (584m/1,916ft), in the southeast; at the northern tip is Megálo Voúno, on the east side Monólithos. The inner wall of the crater falls down to the sea in sheer cliffs, ranging in height between 200m/650ft and 400m/1,300ft, of grayish-black lava with bands of white pumice and reddish tufa. On the outside the land slopes gradually down to the sea in fertile slopes of pumice soil covered with vines. Owing to lack of water the island is treeless. The inhabitants achieve a modest degree of prosperity through the export of pulses, pistachios and tomato purée, and also Santorini earth (pozzolana), a natural hydraulic cement used in structures exposed to water (harbor works, the Suez Canal).
In recent years large numbers of visitors have been attracted to the island by its extraordinary natural structure and its archeological sites, which are among the most important in Greece, and the tourist trade has made an increasing contribution to the economy. But this is not an island for an ordinary seaside holiday, particularly for visitors with children.
In antiquity Thera was known as Kalliste (the "fairest" island) or Strongyle (the "round" island).
Thera was inhabited, probably by Carians, in the third millennium B.C. (Cycladic culture). Achaean Greeks settled on the island about 1900 B.C., but were later driven out by the Phoenicians. The excavations at Akrotíri have shown that Santorini was a flourishing and prosperous island in the first half of the second millennium B.C. It was in contact with Minoan Crete but had developed a distinctive culture of its own. It seems likely that at least the city of Akrotíri was ruled not by some central authority but by a plutocracy of merchants and shipowners who had trading links reaching as far afield as Libya. This trade, and perhaps also an ethnic connection with North Africa, can be deduced from the wall paintings, of astonishingly high quality, which are at present in the National Archeological Museum in Athens.
The golden age ended with the eruption of the volcano around 1510 B.C., which turned the center of the island into a gigantic crater. The suggestion by Spyridon Marinatos that this catastrophe also brought about the end of the Minoan cities on Crete has not been generally accepted.
It has been speculated that the legend of the disappearance of the island kingdom of Atlantis under the sea might be associated with the eruption.
After the eruption the island remained uninhabited for 500 years, until the beginning of the first millennium B.C., when it was resettled by Dorian (Minoan) incomers from Crete, who established themselves on a limestone ridge southeast of Mt Profítis Ilías. In 630 their king, Grinos, founded a colony at Kyrene - the largest Greek colony in North Africa. Allied with Sparta at the beginning of the Peloponnesian War, Thera was obliged to pay tribute to Athens from 427/426 B.C. onwards. It enjoyed a measure of prosperity under the Ptolemies, when an Egyptian garrison was stationed on the island. Thereafter it came under Roman rule.
In 1207, after the fourth Crusade, Santorini was conquered by Marco Sanudo, Duke of Náxos, and remained in Italian hands for three centuries, until its capture by the Turks in 1539. It was reunited with Greece in 1830.
The volcanic force which originally built up the island round the older limestone cone of Mt Profítis Ilías and later destroyed it continued to manifest itself in later centuries. The last violent volcanic phenomena, combined with earth tremors which caused considerable damage, occurred in 1956.