The Panoply: How was Leaning Tower of Pisa built?

Many of us know the science behind Leaning Tower of Pisa. But very few amongst us actually know how the tower was built. So here is a brief info about this World wonder.

The first foundation stone for Leaning Tower of Pisa was laid down in August 1173. The construction came to an halt when three stories were built by the end of 1178. The construction was flawed from the beginning since it was unknown to the architect that the area had once been a large river delta which had sand deposits, making the area unsuitable for large, heavy buildings.

By the time the construction was resumed in 1272, the tower had already started to lean towards south because of unsteady subsoil and mere 3 meter depth foundation. To compensate for this tilt, the engineers built upper floors adding counter weights on the north and halt the further leaning towards south. After the completion of 6 floors, the construction was halted again in 1284.

The seventh floor was completed in 1319 and construction was subsequently completed in 1372 by adding the bell chamber. It took around 200 years to complete the construction of this unique tower! It took so long because the Pisans were engaged in constant battles with Genoa, Lucca and Florence, which halted the tower's construction.

Since its completion the tower has continued to lean at a constant rate. Various surveys and tests conducted regarding this tilt in 1990 suggested that the tower would collapse by the middle of the 21st century. Since then attempts are being made to prevent further leaning.

Tons of Lead counter weights are placed on the north base of the tower to prevent its leaning towards south.

lead weights

An unique solution suggested by English engineer John Burland to extract sandy soil from underneath one side of the tower, was adopted to halt the leaning. It took engineers nearly 2 years to remove 70 metric tons of sand from underneath the raised end before announcing that the tower has been restored to its 1838 position (tilt reduced by 45 cms). They also stated that

it would be stable for at least 200 years.