The cathedral suffered fourteen hits by aerial bombs during World War II. Badly damaged, it nevertheless remained standing in an otherwise completely flattened city.
The German city of Cologne was bombed in 262 separate air raids[1] by the Allies during World War II, all by the Royal Air Force (RAF). A total of 34,711 long tons of bombs were dropped on the city by the RAF.[2] 20,000 civilians died during the war in Cologne due to aerial bombardments.[3]
While air raid alarms had gone off in the winter/spring of 1940 as British bombers passed overhead, the first bombing took place on 12 May 1940.[4] The 30/31 May 1942 attack on Cologne was the first 1,000 bomber raid.
正在欧洲旅游。英法的那些用方块垛子建造的建筑物太宏伟了。这种东西不像现代的水泥，似乎还能雕刻。查了一下，水泥是在公元1800左右发明的。这个时期中国的建筑似乎还是砖木结构，没法造的这么高大坚固。我有个1926年建造的房子。一次把后院门的台阶打碎，灰白色，不像现代水泥那么硬，应该也是那种材料。
The cathedral suffered fourteen hits by aerial bombs during World War II. Badly damaged, it nevertheless remained standing in an otherwise completely flattened city.
https://en.wikipedia.org/wiki/Cologne_Cathedral
The German city of Cologne was bombed in 262 separate air raids[1] by the Allies during World War II, all by the Royal Air Force (RAF). A total of 34,711 long tons of bombs were dropped on the city by the RAF.[2] 20,000 civilians died during the war in Cologne due to aerial bombardments.[3]
While air raid alarms had gone off in the winter/spring of 1940 as British bombers passed overhead, the first bombing took place on 12 May 1940.[4] The 30/31 May 1942 attack on Cologne was the first 1,000 bomber raid.
https://en.wikipedia.org/wiki/Bombing_of_Cologne_in_World_War_II
说是某个人的善心，在一千架轰炸机的轰炸里面，渺小了许多。
这篇文章说，罗马混凝土里面有生石灰，这样出现裂缝进水后，生石灰遇水有自我补救的功能。
https://www.scientificamerican.com/article/ancient-roman-concrete-has-self-healing-capabilities/
Mineral deposits called “lime clasts” found in ancient Roman concrete give the material self-healing capabilities