History of Cologne was considered a substitute for the German University of Strasbourg, which became part of France along with the rest of Alsace. Cologne prospered during the Weimar Republic and progress was made especially in governance, city planning and social affairs. Social housing projects were considered exemplary and were copied by other German cities. As Cologne competed to host the Olympics, a modern sports stadium was erected at Müngersdorf. Beginning of the 1920s civil aviation was permitted once more, and Cologne Butzweilerhof Airport soon became a hub for national and international air traffic, second in Germany only to Berlin Tempelhof Airport. At
Cologne City Hall gradually changed from a mainly feudal society to free citizens. Documents from the years 1135 and 1152, recorded "a house in which citizen convene", referring to the first established council hall, at the location of today's town hall. The coat of arms of Cologne, first mentioned in 1114, is Europe's oldest municipal coat of arms. By 1180, the citizens of Cologne won a legal battle against Philip I, Archbishop of Cologne, for another extension of Cologne's city walls. With the Battle of Worringen fought in 1288, Cologne became independent from the Electorate and on 9. September 1475 officially gained Imperial