During the late Middle Ages and throughout the Renaissance, Venetian artisans rediscovered the ancient secrets of glass making. On the island of Murano, they created superb vessels and jewelry which were valued throughout the known world. It was also during this period that Venice became the most powerful trading nation in Europe, a city whose ships visited every port both east and west. Venetian traders used glass beads for barter, and these jewels became especially prized in Africa, where they were traded for gold, ivory, rare woods and spices. Venetian beads quickly became a medium of exchange throughout Africa, and in some tribes were used as a bridal dowry.