比萨斜塔之所以是倾斜的原因是因为在建造过程中发生了地基沉降。
这座建筑始建于12世纪，建造过程中使用了软土和沙质地基，导致了整个建筑物的倾斜。
由于这个倾斜的角度越来越大，为了防止比萨斜塔倒塌，曾经进行过多次的修复和加固。
这座斜塔的倾斜现在被认为是它的独特之处，成为了世界上最知名的建筑之一。
The Leaning Tower of Pisa is leaning due to the settlement in its foundation during the construction. The tower was built in the 12th century on soft clay and sandy soil, causing the entire structure to lean. As the tilt increased over time, multiple restoration and reinforcement works were carried out to prevent the tower from collapsing. The leaning of the tower is now considered its unique feature and has made it one of the most famous buildings in the world.