On this day in 1990, the Leaning Tower of Pisa was closed to the public for the first time in its 800-year existence amid concerns that it was about to collapse.

At that time, the top of the tower stood at a tilt of 16 feet (4.9m) off the perpendicular, and was measured to have moved 9.6 inches over the course of the previous century.

The tower – actually the campanile, or bell tower, of Pisa’s cathedral – had been tilting a further one-twelfth of an inch (2mm) every year, thanks to being built on ground too soft on its south side to support its full weight.

Building work on the tower began in 1173; it started to sink during the construction of its second tier just five years later. The structure was completed nearly 200 years later, with the addition of the bell chamber in 1372.

19th Century engraving

Attracting over one million visitors each year, the tower’s closure would have a significant adverse effect on the city’s tourism industry.

However, after two decades of stabilisation studies, and spurred by the abrupt collapse of the Civic Tower in the city of Pavia in 1989, experts deemed the closure necessary with the tower leaning at an angle of 5.5 degrees.

Work on Leaning Tower of Pisa

The Italian government allocated 100 billion lire (then £47million) for reconstruction, appointing an international team of engineers to develop a plan for stabilising the tower. Restoration work began in earnest the following year.