From 1815, the independent and sovereign city of Hamburg was a member of the
German Confederation – the association of Central European states created by the
Congress of Vienna – but not a member of the
German Customs Union. Following the
Austro-Prussian War which established Prussian hegemony in North Germany, Hamburg was obliged to join the
North German Federation. However it obtained an opt-out in the form of Article 34 of the North German constitution, which stated that Hamburg and the other Hanseatic cities would remain as free ports outside the Community customs border until they apply for inclusion. Article 34 was carried over into the imperial constitution of 1871, when the south German states joined the federation. However, Hamburg came under great pressure from Berlin to join the Customs Union after 1879, when the latter's external tariff was greatly increased. In 1881 an agreement was signed between the Prussian Finance Minister
Karl Hermann Bitter and the State Secretary of the imperial Treasury, on the one hand, Hamburg's Plenipotentiary Senators Versmann and O'Swald, and the envoy of the Hanseatic states in Berlin, Dr Krüger, on the other. Hamburg would
join the Customs Union with all its territory, except a permanent free port district which the agreement specified. For this district, Article 34 would still apply, thus the freedoms of that district could not be abolished or restricted without Hamburg's approval. In 1991 it was listed as a protected Hamburg heritage site. Since 2008, it has been part of the
HafenCity quarter. In an attempt to revitalize the inner city area, the
Hamburg government initiated the development of the
HafenCity area, for example with the construction of the
Elbe Philharmonic Hall. ==Architecture==