Britain had long been known to the classical world as a source of tin. The coastline had been explored by the Greek geographer Pytheas in the 4th century BC, and may have been explored even earlier, in the 5th century, by the Carthaginian sailor Himilco. But to many Romans, the island, lying as it did beyond the Ocean at what was to them the edge of the known world, was a land of great mystery. Some Roman writers even insisted that it did not exist, and dismissed reports of Pytheas's voyage as a hoax.