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
Historical Archive of the City of Cologne so-called White Book ("Weißes Buch"), a book of copies of charters and privileges. By 1370 the archives were located in the "Haus zur Stessen". In medieval Cologne, valuable goods and important trade documents were frequently stored in vaulted warehouses specially built in backyards. This method of storage was used by both business owners and the municipal administration. Documents included grants of privileges, contracts, records of lawsuits, maps, seals and documents from the estates of important persons. As the city and its national and international trade thrived and prospered, the municipal administration began to plan further storage to house the growing