Kölner Grüngürtel

After the Congress of Vienna, the Prussian military administration turned Cologne into a fortress city – on the left bank from 1816 to 1846, around Deutz from 1818 to 1863. In front of the bastions lay 14 forts and nine smaller lunettes, replaced from 1873 by an outer ring of eleven forts. Around 1900 Cologne was considered the largest fortress in the German Empire. Yet the fortifications blocked the urgently needed expansion of the city and were becoming militarily obsolete. In 1907 the city bought the fortress area from Prussia for 23 million Reichsmark. The inner fortress ring survived until the end of the First World War and was then razed under the Treaty of Versailles.

The Inner Green Belt runs about seven kilometres from the Rhine at Köln-Riehl to Luxemburger Straße; its landmarks include the Friedenspark around Fort I, the Rosengarten around Fort X and the four-hectare Aachener Weiher. The Outer Green Belt extends beyond the city limits of the time and covers around 800 hectares, 400 of them forest, threaded by the Militärring and accompanied by footpaths and cycle paths. Bodies of water such as the Decksteiner Weiher, the Kalscheurer Weiher and the Adenauerweiher are embedded within it.