lready grown to 700,000 inhabitants. Industrialization changed the city and spurred its growth. Vehicle and engine manufacturing were especially successful, though heavy industry was less ubiquitous than in the Ruhr area. The cathedral, started in 1248 but abandoned around 1560, was eventually finished in 1880 not just as a place of worship but also as a German national monument celebrating the newly founded German empire and the continuity of the German nation since the Middle Ages. Some of this urban growth occurred at the expense of the city's historic heritage with much being demolished (for example, the city walls or the area around the cathedral) and sometimes replaced by present-day buildings.
Cologne was designated as one of the Fortresses of the German Confederation. It was turned into a heavily armed fortress (opposing the French and Belgian fortresses of Verdun and Li�ge) with two fortified belts surrounding the city, the remains of which can be seen to this day. 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 in a very dense built-up area within the city itself.
During World War I Cologne was the target of several only minor air raids and survived the hostilities without significant damage. Until 1926 Cologne was occupied by the British Army of the Rhine under the terms of the armistice and the subsequent Versailles Peace Treaty. Contrary to the harsh measures taken by French occupation troops, the British acted with more tact towards the local population. The mayor of Cologne from 1917 until 1933 and future West German chancellor Konrad Adenauer acknowledged the political impact of this approach, especially that the British had opposed French plans for a permanent Allied occupation of the Rhineland.
As part of the de-militarization of the
