The accession of the city state of Hamburg to the German Customs Union, commonly known as Zollverein, in 1888 (along with Bremen) was the culmination of a project for the economic and monetary union of Germany, stretching back to 1819. In that year Schwarzburg-Sondershausen joined Prussia’s internal customs union, the first other state to do so and the first of many to follow. When the German Customs Union (Deutscher Zollverein) was initially formed, in the 1830s and 1840s, the motives of the states in joining did not include any particular desire to unite with others to form a wider more powerful entity. The states which joined fought vigorously against any impairment of their full sovereignty. Hence each member had a veto and the union was not permanent, but had to be renewed after 12 years. Each member sought its own economic advantage. Accordingly, the accession of any of the Hanseatic cities of Hamburg, Bremen or Lübeck would have to be on condition that accession served the city's own advantage. A pre-condition of such advantage was that their territory touched directly with that of the Customs Union, which only happened for Hamburg after 1854, when Hanover joined. However Hamburg kept an open frontier with Holstein until 1867, when it was included in the Customs Union on being annexed to Prussia. But, after these accessions, other factors came into play as regards the question of Hamburg joining. Origins of Free Trade in Hamburg In 1189 the Holy Roman Emperor Frederick Barbarossa granted Hamburg the status of an Imperial Free City and tax-free access along the Lower Elbe into the North Sea, free of any tariffs and duties, etc. The rights were given orally for Hamburg's support of Frederick's participation in the crusades. The written charter containing these rights, although dated 7 May 1189, actually originated in the 1360s, during a dispute between Hamburg and the Archbishop of Bremen over duties on the Elbe. In the year 1038, the emperor Conrad II granted rights to the Archbishop of Bremen to establish a fair at Stade, a small town on the Elbe 25 miles below Hamburg. This included the right to charge duties on commodities for sale at the fair or landed at Stade for that purpose. The Archbishops abused this privilege and, purporting to have a compulsory market at Stade, exacted a duty on all vessels passing by that town. However, the citizens