The first stone of the iconic monument was laid on August 9, 1173, “thanks to the donation of 60 coins made by a widow named Berta, for the construction of the bell tower of our cathedral,” the Archbishop of Pisa, Giovanni Paolo Benotto, said during a press conference on Wednesday, outlining events to celebrate the anniversary.

But the birthday might never have even happened, given, for some time, it was feared the much-loved tower was in danger of toppling over.

In the early ‘90s, the crowning glory of a significant UNESCO World Heritage site, reached a lean of 5.5 degrees.

Understandable concerns for its stability led to an international effort to stop it from literally hitting the dirt, with work lasting eight years from 1993.

When work completed in 2001, the lean had been restored to a palatable 3.97 degrees.

“Today the bell tower is a stable monument,” Andrea Maestrelli, the president of Opera della Primaziale Pisana (OPA), the 1000-year-old body that looks after the cathedral complex that includes the tower, said at the press conference.

Interestingly, according to Wikipedia, the tower has survived at least four strong earthquakes since 1280.

A 2018 engineering investigation concluded that the tower withstood the tremors because of dynamic soil-structure interaction: the height and stiffness of the tower combined with the softness of the foundation soil influences the tower’s vibrational characteristics in such a way that it does not resonate with earthquake ground motion.

Therefore, in something of an irony, the same soft soil that has caused the leaning and brought the tower to the verge of collapse, has helped it survive.

The 850th birthday celebrations will include free entry to all the monuments in Pisa’s Piazza del Duomo, except the Tower which is being lit up and will be closed for security reasons, from 10.30pm until midnight.

There will also be a free concert by Iranian pianist Ramin Bahrami featuring pieces by Bach, Beethoven, Mozart, Brahms and Chopin.

A series of initiatives are also planned over the next 12 months to mark the Tower’s big anniversary.

ANSA