The naming of the Sargasso Sea for its "Sargassum" seaweed dates from the early 15th-century Portuguese explorations of the Azores Islands and of the large "volta do mar" (the North Atlantic gyre), around and west of the archipelago, where the seaweed was often present. However, the sea may have been known to earlier mariners, as a poem by the late 4th-century author Rufus Festus Avienus describes a portion of the Atlantic as being covered with seaweed, citing a now-lost account by the 5th-century BC Carthaginian Himilco the Navigator.