The slave trade in Western Europe also existed in the Middle Ages. In addition to the Scandinavian Vikings, Italian merchants from Genoa and Venice, the Portuguese imported slaves. The Irish city of Dublin in the eleventh century was the largest slave market in Western Europe. The gradual transition from slavery to serfdom lasted for several centuries. Slavery was permitted by law, but the Christian Church actively opposed enslaving fellow believers into slaves. Muslim Spain Al-Andalus imported huge quantities of slaves and served as a staging post for sending slaves to Muslim countries.