A small village at the location of Dortmund was mentioned in official documents from 880 to 885 as Throtmanni. After it was destroyed by a fire, the Holy Roman Emperor Frederick I (Barbarossa) had the town rebuilt in 1152 and resided there for two years. It became an Imperial Free City in 1220. During that century, it was the "chief city" of the Rhine, Westphalia, the Netherlands Circle of the Hanseatic League.
After 1320, the city appeared in writing as "Dorpmunde", and the 1661 earthquake collapsed the Reinoldikirche. Within the Prussian Province of Westphalia, Dortmund was a district seat within Regierungsbezirk Arnsberg until 1875, after which it was an urban district within the region. During the industrialization of Prussia, Dortmund became a major centre for coal and steel.
Under Nazi Germany, the synagogue was destroyed in 1938. Also, the Aplerbeck Hospital in Dortmund transferred mentally and/or physically disabled patients for euthanasia at the Hadamar mental hospital as part of the Action T4 (an additional 229 children were killed in the "Children's Specialist Department", which was transferred from Marburg in 1941). Dortmund bombing targets of the Oil Campaign of World War II included Hoesch-Westfalenh�tte AG, the "Hoesch-Benzin GmBH" synthetic oil plant, and the Zeche Hansa coking plant; and bombing destroyed about 66% of the Dortmund homes and about 98% of the inner city area. The code word Dortmund was radioed to initiate the 1941 Operation Barbarossa campaign against the Soviet Union.
The Allied ground advance into Germany reached Dortmund in April 1945. The US 95th Infantry Division, attacked the city on 12 April 1945 against a spirited German defense. The division, assisted by close air support, advanced through the ruins in urban combat and completed its capture on 13 April 1945.
Post-war, buildings such as the Reinoldikirche and Marienkirche (churches) were restored/rebuilt, and extensive parks and gardens were laid
