Leaning Tower of Pisa

Construction began after a bequest: on 5 January 1172 a Pisan widow, Donna Berta di Bernardo, left sixty soldi toward the campanile fund, and the foundations were laid on 9 August 1173. The circular white marble ground floor, a blind arcade of engaged columns with Corinthian capitals, went up during a period of Pisan military success and prosperity. Its architect is disputed: tradition, as recorded by Vasari, credited Bonanno Pisano, a bronze-caster active in Pisa who left for Sicily in 1185 and later returned to die in his home city, working alongside a builder named Guglielmo. A stone bearing Bonanno's name was found near the tower's base in 1820, though it may instead be linked to the cathedral's bronze door destroyed in 1595; a 2001 study points instead to Diotisalvi, builder of Pisa's baptistery and the bell tower of San Nicola.

The tower began sinking once building reached the second floor in 1178: its foundation was only about three metres deep, set in weak subsoil, a flaw built in from the start. Work stopped for close to a century while Pisa fought Genoa, Lucca and Florence, giving the ground time to settle and, most likely, saving the half-built tower from collapse. Building resumed in 1272 under Giovanni di Simone, who built the upper floors taller on one side to compensate for the lean, leaving the tower visibly curved; it stopped again in 1278 after Pisa's defeat by Genoa at the Battle of Meloria. The seventh floor was finished in 1319, and Tommaso di Andrea Pisano added the Gothic bell chamber in 1372, closing 199 years of intermittent construction.

Galileo Galilei, living in Pisa at the time, is said to have dropped two cannonballs of different masses from the tower between 1589 and 1592 to show that they fell at the same speed regardless of weight. The claim rests on a single account by his pupil and secretary Vincenzo Viviani, written in 1654 but not published until 1717 — well after Galileo's death — so it is recorded as tradition rather than an eyewitness record from the time.

During the Second World War the Allies suspected German forces were using the tower as an observation post. Sergeant Leon Weckstein of the US Army was sent to confirm whether German troops occupied it; struck by the beauty of the cathedral and its campanile, he chose not to call in an artillery strike, leaving the tower undamaged.

Nineteenth-century restoration under Alessandro Gherardesca exposed the tower's base between 1838 and 1839, disproving the theory that it had been built leaning on purpose — but the excavation also struck a large body of groundwater beneath the foundation. Pumping the water out to keep working made the surrounding soil subside further, increasing the tilt. In 1934, on the orders of Benito Mussolini, who called the tilt a 'national shame', workers drilled into the base to inject cement in an attempt to straighten it; the operation went wrong, causing the tower to sway dangerously before settling into a lean worse than before.

By 1990 the tilt had reached 5.5 degrees and, spurred by the sudden collapse of the Civic Tower of Pavia in 1989, Italy closed the tower to the public on 7 January 1990. Its bells were taken down, cables anchored the third level to fixed points hundreds of metres away, and nearby residents in the collapse path were evacuated. From 1993, engineers added several hundred tonnes of lead counterweights to the north side, and between 1999 and 2001 they extracted 38 cubic metres of soil from beneath the raised end, reducing the tilt by 45 centimetres to roughly its 1838 angle. The tower reopened on 15 December 2001, its lean reduced to 3.97 degrees and declared stable for at least 300 years.

The tower, cathedral, baptistery and cemetery of the Piazza del Duomo were inscribed as a UNESCO World Heritage Site in 1987, and the tower itself carries Italian national heritage protection; it is owned and managed by the Opera della Primaziale Pisana, the body responsible for all the square's monuments. In May 2008 engineers announced that the tower had stopped moving for the first time in its recorded history and judged it stable for at least 200 years. A ceremony marking the 850th anniversary of the laying of its foundation stone was held on 9 August 2023.