The Garisenda Tower in Bologna is not as famous as the Tower of Pisa, but it leans a little more. Lately, though, the dynamic of its movement has become worrisome, and city officials decided recently that the central square where it stands a few meters apart from the much taller Asinelli Tower will be closed off, most likely for years.
The tower, which, along with the Asinelli Tower, makes up the “two towers,” a symbol of the city, has historically slanted four degrees. But recent surveys have found traces of unexpected rotation in its incline and other imperceptible movements that need to be studied more carefully, the authorities said.
“The point is not that the tower is collapsing,” Mayor Matteo Lepore of Bologna said in a phone interview. “We have been monitoring it since 2018 like a patient in a hospital, and we know now that it needs to be secured and restored, and decided to start immediately.”
He explained that the area was closed off last week to allow a more thorough monitoring of the site, possible only without traffic noise and interference.
For years, a committee of national experts has been studying the data collected from the Garisenda Tower, thanks to acoustic sensors, optical fibers, a GPS on its top, a pendulum and systems to monitor the water table that runs underground, close to the tower. In 2021, the base of the tower was completely encircled with large iron rings to prevent any cracks in its fragile selenite stone. Since the late 1990s, other iron rings have been used to reinforce the upper portion of the tower, made of typically Bolognese red bricks.
The ground and the tower’s foundations started sinking after construction in the early 1100s, probably because of a construction error, and in the middle of the 1300s, the tower was shortened over fears that it could collapse. Its “leaning forward” scared even Dante Alighieri, who in “Inferno,” the first volume of his “Divine Comedy,” compared it with the appearance of a giant, Antaeus.
Like all towers and skyscrapers, the Garisenda Tower has always swayed slightly. Even within the experts’ committee, geologists, engineers, architects and chemists have not had the same perception of the problem and its solutions.
“Everybody agrees that the base needs to be reinforced, because of its historical weakness and because of the recent concerns raised by the data collected,” said Cleto Carlini, who is in charge of public works, green spaces and mobility at Bologna’s City Hall.
“The question is how, and we need to study that thoroughly before planning the restoration,” he explained.
In past years, experts advised building a series of tall piers with steel cables able to hold the tower and avert possible worsening of the tilting. But the project was aborted because of fears that digging the piers’ deep foundations could affect the stability of the nearby Asinelli Tower, the mayor said.
A later restoration plan envisioned injecting a special kind of cement into the base to fill in the gaps generated in the selenite over time. But it didn’t move forward because experts deemed that more tests were needed before the project could be carried out.
Now that the area has been cordoned off, the plan is to build bulkheads around the tower’s base to secure it. Later, the tower, which is about 157 feet, or 48 meters tall, will be wrapped in a protective box as a restoration strategy is chosen.
Mr. Lepore said it was not yet clear whether experts would try to straighten out the tower, solidify its base or even try taking some of it apart to rebuild the structure more solidly. He promised that the tower’s safety net would be erected in six months.
The restoration of the Garisenda Tower will take much longer: years, he said. Others said it could take up to a decade.
The closing of the center is already affecting traffic and is happening as work to build one of two new tramway lines has already begun in the same area.
The mayor hopes to take the opportunity to “redesign mobility in the city and make it more pedestrians-only,” he said.
In 2021, the city’s roughly 39 miles, or 62 kilometers, of porticoes became a UNESCO world heritage site. Bologna is now hoping to extend the protected area to include the Garisenda Tower and Asinelli Tower, which, at 318 feet, or 97 meters, is the tallest leaning tower in Italy. The Asinelli has historically tilted 1.3 degrees, much less than the Garisenda and, in recent years, even opened to tourists who were able to walk up its 498 steps It is now closed, and monitoring systems have been increased on this tower as well.
In the Middle Ages, aristocratic and wealthy families built towers to show their power to competing residents, and many Italian cities, including Bologna, had dozens of them, including these two.
“Having the two towers on the UNESCO list would help us in terms of promotion and visibility,” Mr. Lepore said, “but also in terms of maintenance and preservation for the future.”
Tourism has grown exponentially in the busy and buzzing northern city in recent years, he said.
Some in the far-right national government have accused the left-leaning administration of Bologna of failing to act fast enough on the Garisenda Tower. But Italy’s culture minister, Gennaro Sangiuliano, has vowed to work together on the restoration and beyond.
Lucia Borgonzoni, Italy’s deputy culture minister, who is from Bologna, said that the ministry would set aside 5 million euros, or $5.3 million, in funds to restore the tower. Other government members have raised the figured to 10 million euros.
“We also hope to attract foreign investors and benefactors,” Mr. Lepore said. “Our towers are a symbol of Bologna, just like the porticoes.”