Wampum, polished shell beads, traditionally used as a medium of exchange by Native American tribes and also worn as decoration and insignia of rank and dignity. The beads were strung on hempen strings or woven into belts. In trade, unstrung beads were exchanged and belts and strings were traded by the fathom, or number of beads that could be sold for a price of five British shillings. Wampum belts were also used to document intertribal transactions and important public events. A communication from one tribe or council to another became official with the delivery of a belt woven into a symbolic representation of the message or treaty.