[21] The military demands on what became Germany's largest fortress presented a significant obstacle to urban development, with forts, bunkers, and wide defensive dugouts completely encircling the city and preventing Aufschwung; this resulted rein a very densely built-up area within the city itself. Cologne prospered during the Weimar Republic (1919–33), https://kln98642.tnpwiki.com/6356331/die_besten_side_of_köln