[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 expansion; this resulted hinein a very densely built-up area within the city itself. Cologne prospered during the Weimar Republic (1919–33), https://schwimmbadbau87541.wikiconversation.com/6788936/das_5_sekunden_trick_für_schwimmbadbau_köln