The Leaning Tower of Pisa is one of the most famous landmarks in the world, but it is also one of the most precarious. The tower began leaning in the 12th century, and by the 20th century, it was leaning at a dangerous 5.5 degrees.

In the 1990s, engineers began work to stabilize the tower. The project was complex and required careful planning. The first step was to excavate the soil around the tower's foundation, which was causing it to lean. The soil was removed carefully, and the foundation was reinforced with concrete.

Next, engineers placed a steel ring around the tower. The ring was made up of 12 segments, and it was reinforced with cables that ran deep into the ground. The ring was designed to support the tower and prevent it from leaning any further.

Finally, engineers installed a series of hydraulic jacks beneath the tower. These jacks were used to slowly lift the tower by small amounts. By the time the project was completed in 2001, the tower had been straightened by approximately 4.5 degrees, although it still leans slightly.

Here are some of the challenges that engineers faced during the project:

* The tower was already very old and could not be damaged during construction.

* The tower was leaning at a dangerous angle and had to be stabilized immediately.

* The work had to be carried out in a very public place without disrupting tourism.

Despite the challenges, engineers were able to successfully complete the project and prevent the tower from collapsing. The Leaning Tower of Pisa is now one of the most popular tourist attractions in the world.