the customs frontier. The free port was extended several times. Initially it had an area of 3.9 sq. miles By 1970 it had an area of 5.6 sq. miles. The free port was closed on 1 January 2013, at which time it had an area of 6.3 sq. miles, which was 23% of the port area. The later additions covered several basins and onshore installations west of the Kohlbrand. Unlike other free ports in Germany, the Hamburg free zone had manufacturing, assembly and other processing operations, whether or not using imported materials. The Hamburg Free Port administration would give approval depending on whether the end products were primarily, although not necessarily exclusively, for re-export. Processing might be approved, even if it should lead to placement of goods in a more favourable tariff classification than at the time of entry into the zone. Customs surveillance was carried out by the Freihafenamt (Free Port Authority), rather than by the regular customs department. This authority, an arm of the state of Hamburg, which owned the land, leased the land in the free zone to private operators. The old Free Port section included most of the city's shipyards. The zone's newer area west of the Kohlbrand included petroleum storage and extensive container terminal facilities. The Free Port had numerous warehouses, transit sheds, grain handling facilities, facilities to handle tropical fruit, raw tobacco, coffee, fish, edible oils, timber, coal and other products. See also Timeline of Hamburg history (extended version) Notes References Borowsky,Peter. Hamburg and the Freeport - Economy and Society 1888–-1914, publ Hamburg University Press, Hamburg, 2005 Clapp, Edwin J. The Port of Hamburg, publ.Yale University Press, New Haven, Conn., 1911 Henderson, William. The Zollverein. Publ Cambridge University Press, 1939 Hutt, William, MP. Stade Duties Considered, publ by J. Ridgway (printer: Brettell), London 1839 Keller, Wolfgang and Shiue,Carol (University of Colorado, NBER, and CEPR) The Trade Impact of the Customs Union, Pub. University of Colorado, 5 March 2013 Malet, Sir Alexander (former British Envoy Extraordinary and Minister Plenipotentiary at Frankfort). Overthrow of the Germanic Confederation by Prussia in 1866, publ. Longmans, London, 1870 Ploeckl, Florian. The Zollverein and the Formation of a Customs Union, Discussion Paper no. 84 in Economic and Social History series, publ by Nuffield College, Oxford;Page 23; Retrieved from www.nuff.ox.ac.uk/Economics/History March 2017 Roghé, Eduard. Anschluss Hamburgs und Bremens an das Deutsche Zollgebiet, Publ.Verlagsanstalt und Druckerei A.-G., Hamburg, 1890 (Staats- und Universitätsbibliothek