During the Middle Ages, the Hanseatic League, uniting towns around the Baltic Sea, formed the most dominating trading bloc in the world. Tallinn was a member of The Hanseatic League (The Hanseatic League was an alliance of trading guilds that established and maintained a trade monopoly over the Baltic Sea, to a certain extent the North Sea, and most of Northern Europe for a time in the Middle Age.) Since this ancient time Tallinn has been developing as a gateway between East and West.