In the Middle Ages the trade between the North Sea and Baltic Sea grew dramatically, but the sea journey through Øresund, increasingly important to commercial shipping since the thirteenth century, was time-consuming and dangerous. Therefore, the emerging Hanseatic city of Lübeck and Eric IV of Saxe-Lauenburg agreed in 1390 to cooperate in the construction of an artificial canal between the Elbe and the Baltic Sea. Construction on the canal began in 1391; thirty barges carrying the first load of salt from Lüneburg reached Lübeck on 22 July 1398.