比萨斜塔“斜而不倒”的秘密

C.Caputo

比萨斜塔是世界建筑史上的一大奇迹。由于塔身压力过重和地质松软，其南面的地基比北面约低2米。在施工期间，塔身即出现轻微倾斜，随着工程进度的推进，倾斜度不断增加，比萨斜塔曾一度停工。

When you hear the word“Pisa”,you immediately think of the Leaning（倾斜）Tower.Although it's famous now, its creators never intended it to be. It was supposed to be a straightforward bell tower behind a cathedral.Today it is considered one of the wonders of the medieval（中古的）world.

So what happened to change the plan? Well, the construction began in 1173. Things progressed a little more slowly back then. It took five years to complete the first three floors. And during those years,the tower stood perfectly straight.

But then,after the third floor was finished,the weight of the structure became just too heavy for the foundation beneath it. The foundation was less than 10 feet deep and it was built with clay, sand, and shells from nearby rivers.In fact,Pisa got its name from a Greek word meaning“marshy”（湿地的）.

The ground under the tower settled unevenly（不平坦地）,with the south side of the tower settling more than the north side.As a result,the tower started to lean toward the south. Builders stopped the construction once they realized it, but unfortunately there was no time to worry about it. War broke out between Pisa, where the tower is located, and another Italian city-state called Genoa. The construction stopped for almost a century! It turned out that the delay was a good thing. Had the tower been completed, it probably would have collapsed.

The construction continued in 1272. The 7th floor was finished in 1319 and the bell chamber was added in 1372. Then in 1990, the tower was closed to tourists. Engineers were able to reduce the lean and stabilize it.The tower reopened in 2001.

In 2008, sensors showed that the lean has stopped increasing. Engineers now believe that it should remain stable for hundreds of years.So if Pisa is on your bucket list,you should be able to visit the tower for years to come. And while you're there, check out some of the other leaning towers in Pisa. Because they are all built on the same soft ground, there are several other towers in Pisa that all lean one way or the other!