In 1648 the dominions of the Bremen archbishopric passed to Sweden, who continued this toll as an established customary right. As this was disputed, in 1691 a Convention to regulate the toll was agreed between Hamburg and Sweden. In 1725, the territory and the toll passed to the Electorate (later Kingdom) of Hanover, who enforced the collection with a ship at Brunshausen on the Elbe, at its confluence with the tributary river Schwinge. Despite the exemption for Hamburg's ships, this toll was a great inconvenience to commerce and in 1861 Hanover agreed by treaty to abolish the toll in exchange for compensation, one third provided by Hamburg, one third by Britain and one third by other countries affected. Thus was brought about toll free access for Hamburg's trade. Bremen had similar interests to Hamburg, but because of its more westerly position, it was affected by competition from the Dutch ports. These gained advantage from the trade treaty made in 1839 between the German Customs Union and Holland. To avoid this problem, the Senate of Bremen made two proposals in 1839 and 1842 to extend the Customs Union to the coast. They not only proposed the elimination of the differential duties in favour of Holland, but also the imposition of a protective duty on all goods imported by non-union ships, the establishment of joint consulates for the protection of economic interests abroad, which up to that time could only be very deficient due to the large number of different states, and a common trade flag of all the ships belonging to the union. There was some encouragement from Hamburg initially and Prussia was in favour. However, by 1845, when Prussia stated its position, the Senate of Hamburg expressed itself in a memorandum very vigorously against such ideas. It invoked the free-trade argument that every protective tariff is an unjust burden on the many to benefit the few. In this case, in favour to the union vessels, to which all the consumers of imported articles, as well as the exporting producers, would have to pay monopoly prices for sea transport. The Hamburg Senate did not wish to know anything about a common flag either: it was in the interests of the Hanseatic cities that they retain their own flags, and thus present themselves abroad as neutral trade republics, even if German states went to war with other countries. Likewise, joint consulates were unacceptable as it would be difficult for them to represent the multifarious interests of the participating states. Although 1834 is the official date of the Customs Union's establishment, member states in fact joined at various times over several decades.