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A tower in the Italian city of Bologna that is less known than its Pisa counterpart - but leans equally as much - has been sealed off, with authorities saying it’s at high risk of collapse.

Constructions have begun on a 5 metre (16ft) high barrier around the mediaeval Garisenda Tower to contain debris in the event that it falls.

The 47 metre (154ft) 12th Century tower tilts at a four-degree angle but studies have found shifts in the direction of its tilt.

Bologna’s council have said the situation is "highly critical".

The tower is one of two which dominate the skyline of Bologna - both of which lean.

The other tower, the Asinelli, is around twice the height of the Garisenda and doesn’t lean so dramatically. In fact, it’s usually open for tourists to climb.

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The Garisenda was built between 1109 and 1119 and it famously reduced in height in the 14th Century as it had already begun to lean.

The tower is famous beyond Italy - mentioned in poet Dante's work The Divine Comedy, completed in 1321.

The site of the Garisenda was initially closed back in October following sensors picking up the changes in its tilt.

Further inspections revealed deterioration in its base.

The city’s council has explained that, as well as containing potentially falling debris, the barrier being put in place will protect surrounding buildings as well as people if it were to collapse.

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Representatives say the work "represents the first phase of making it safe".

The construction of the barrier is expected to be completed early next year - and the tower itself as well as the plaza beneath it will likely remain closed for a number of years while necessary restoration work is carried out.

Bologna authorities estimate that the barrier alone will cost some €4.3m. They have already launched a crowdfunder to go towards paying for the restoration.

The council called the project an "extraordinary challenge" which will require "commitment from the entire city and from those all over the world who love Bologna and one of its most important symbols".