The golden fleece (aureum vellus) is found in some medieval encyclopedias. It is said to be wool of a metallic golden color, produced by the sea or by a fish or shellfish in the sea. Its color could not be matched by any dye.

The story of the golden fleece is from ancient Greek mythology, known from at least the time of Homer (8th century BCE). It was said to be the fleece of the winged ram Chrysomallos, which was kept in a sacred grove, until Jason and the Argonauts stole it.