The Cassiterides (, meaning "Tin Islands", from κασσίτερος, kassíteros "tin") are an ancient geographical name used to refer to a group of islands whose precise location is unknown, but which was believed to be situated somewhere near the west coast of Europe. Ancient geography Herodotus (430 BC) had only vaguely heard of the Cassiterides, "from which we are said to have our tin," but did not discount the islands as legendary. Later writers—Posidonius, Diodorus Siculus, Strabo and others—call them smallish islands off ("some way off," Strabo says) the northwest coast of the Iberian Peninsula, which contained tin mines or, according to Strabo, tin and lead mines. A passage in Diodorus derives the name rather from their nearness to the tin districts of Northwest Iberia. Ptolemy and Dionysios Periegetes mentioned them—the former as ten small islands in northwest Iberia far off the coast and arranged symbolically as a ring, and the latter in connection with the mythical Hesperides. The islands are described by Pomponius Mela as rich in lead; they are mentioned last in the same paragraph he wrote about Cadiz and the islands of Lusitania, and placed in Celtici. Following paragraphs describe the Île de Sein and Britain. Probably written in the first century BC, the verse Circumnavigation of the World, whose anonymous author is called the "Pseudo-Scymnus," places two tin islands in the upper part of the Adriatic Sea and mentioned the market place Osor on the island of Cres, where extraordinarily high quality tin could be bought. Pliny the Elder, on the other hand, represents the Cassiterides as fronting Celtiberia. At a time when geographical knowledge of the West was still scanty, and when the secrets of the tin trade were still successfully guarded by the seamen of Gades (modern Cadiz) and others who dealt in the metal, the Greeks knew only that tin came to them by sea from the far West, and the idea of tin-producing islands easily arose. Later, when the West was better explored, it was found that tin actually came from two regions: Galicia, in the northwest of Iberia, and Devon and Cornwall in southwest Britain. Diodorus reports: "For there are many mines of tin in the country above Lusitania and on the islets which lie off Iberia out in the ocean and are called because of that fact the Cassiterides." According to Diodorus tin also came from Britannia to Gaul and then