This Day in History: 1990 Leaning Tower of Pisa closed to public

The Leaning Tower of Pisa has been closed to the public for the first time in 800 years amid speculation the structure is on the verge of toppling over.
Over the past 100 years the belfry at the top of the mediaeval tower has moved 9.6 inches (nearly a quarter of a metre).
The tilt is currently 16ft (4.9m) off the perpendicular and increases by about one-twelfth of an inch (2mm) every year because the layer of clay and sand on which it is built is softer on the south side than on the north.
So, the Italian government has set aside 100bn lire (£47m) and appointed an international team of experts to come up with a detailed plan within three months to save the building from collapse.
The 13th century monument, which took more than 200 years to build, attracts in excess of one million visitors each year, many of whom climb to the top to enjoy the panoramic view of Pisa.
The tower’s closure is therefore bound to have a significant impact on the city’s tourism industry.
The eight-storey structure began tilting almost immediately after it was completed in 1350 and although there are no plans to completely straighten it, experts believe urgent work is required to reverse the tilt.
Attempts have been made in the past to stop the building moving. Mediaeval builders tried to correct the tilt but their efforts resulted in the upper section of the tower leaning at a different angle to the lower section.
The Leaning Tower’s ornate and unique exterior balconies were built to enable local dignitaries to be seen by the populace during religious processions in the Middle Ages.

Courtesy BBC News

In context

The Leaning Tower of Pisa did not reopen until 2001.
The first stages of the restoration project began in 1992 and by 1993 the tower had stopped leaning.
However, in September 1995, the medieval monument suddenly lurched 2.5mm (0.09in) in one night – about 10% of the lean that the commission had corrected since 1990.
To prevent this happening again the structure was held up by two steel supports while the stabilising work was completed.
Engineers then placed lead weights on the north side of the tower, and removed tonnes of soil from underneath the building using corkscrew drills – the tower then gradually sunk into the cavity.
By 2001 the lean had been corrected by 45cm at a cost of £200m. But it is predicted that in 300 years the tower will be back at the angle it was in 1990 and on the brink of collapse.
British engineer, Professor John Burland, who oversaw the restoration work said it was hard to explain how the tower had not fallen prior to its closure in 1990.
Computer models suggested it should have toppled once it reached a tilt of 5.44 degrees – but by 1990 it was leaning by 5.5 degrees.