But there was one physical feature which, more than any other, must have impressed the imagination of the dwellers by the Mediterranean shores; and that was furnished by the volcanic phenomena so characteristic of the great depression between Europe and Africa. Among the islands of the Ægean sea, some were continually smoking; others retained, in their cindery cones and ashy slopes, the memorials of subterranean fires not long extinguished. From time to time actual eruptions broke forth, with their accompaniments of convulsion and terror. We know from geological evidence that one of the most violent volcanic explosions which have affected the Mediterranean basin took place where now is the island of Santorin, after the original site was inhabited by a civilised people.[13] A conical volcanic mountain--an eastern Vesuvius or Etna--stood on that site, but in some prehistoric age it was blown into the air, as happened at Krakatoa in August, 1883, only portions of the base of the cone being left to form the present semi-circular ring of islands. Whether this stupendous catastrophe occurred after the Hellenic race appeared in the Ægean area has not been determined. But the tradition of it may have lingered in the district, down to the time when, about two hundred years B.C., a new volcano rose from the sea in the centre of this group of islands. Another marked eruption occurred in the year 46 B.C. Even in our own day, this ancient vent has shown renewed activity, fresh eruptions have taken place from the middle of the engulphed crater, and another central volcanic cone is gradually rising there. The Greeks, thus accustomed to volcanic phenomena among their own islands, were prepared to accept the stories, brought to them from the remote West, of far more colossal volcanoes, and more gigantic and continuous eruptions. Like the accounts of other physical phenomena imported from that distant and half mythical region, the tales of the volcanoes were no doubt at first more or less exaggerated. The adventurous voyagers who, sailing as far as Sicily and the Æolian Islands, saw the noble snow-capped cone of Etna, loftier than the mountains of Hellas, yet emitting smoke by day and a glare of fire by night; who watched Stromboli continually in eruption; who perchance beheld the land convulsed with earthquakes, the air darkened with volcanic dust, the sea covered with floating cinders, and who only with much effort were able to steer their vessels into opener water, would bear eastward with them such tales of horror as would not fail to confirm and increase the popular belief in the national mythology, and might even suggest new myths or new versions of those already current. The greater size and vigour of the volcanoes would tend to create the impression that other characteristics of the region were on a similarly exaggerated scale. Sicily was accordingly believed in Homeric times to be the home of a gigantic race of shepherds--the Cyclops.