Solving the 800-year mystery of Pisa's Leaning Tower - Professor John Burland has spent the last two decades striving to save - and understand - the Leaning Tower of Pisa. After defying gravity, Italian bureaucracy and accusations of corruption, it seems he’s finally cracked the case.
All six donkeys were impeccably behaved. They’d been ridden into Pisa’s main square, the Piazza dei Miracoli, last November by vexed vets from Pisa University and ceremoniously set down beneath its Leaning Tower. In protest at government cuts across Italian education, the profs duly gave an al fresco lecture on donkey anatomy to hundreds of bewildered tourists. Silvio Berlusconi’s photo appeared on many a banner, beside the words ‘The biggest ass of all’.
A view of Pisa's Piazza dei Miracoli (Miracles' square) with the famous leaning tower,
Construction workers remove steel cables known as "suspenders" from the base Leaning Tower of Pisa, central Italy, Tuesday, May 15, 2001
PROF JOHN BURLAND, WHOSE EXPERTISE HELPED SAVE THE LEANING TOWER OF PISA FROM IMMINENT COLLAPSE
Such a display of faculty dissent would have been impossible a decade ago, when the area of piazza around the tower was completely cordoned off. It looked then more building site than World Heritage site and the howls of protest from local Pisans were far louder than a few braying donkeys.
From 1990 to 2001, the tower remained closed – many doubting it would ever reopen – as the International Committee for the Safeguard of the Leaning Tower strove to save it from collapse. Visitors to Pisa dropped off by 45 per cent.
‘The street vendors were furious about lost trade and demanded the tower be reopened,’ says John Burland, the only Brit on the 14-man committee. ‘But it was close to toppling over. Without our intervention, any local storm or earth tremor could have finished it off.’ Burland, 72, is emeritus professor of soil engineering at Imperial College London, his reverend-like humility belying the fact that he helped solve one of the most fascinating riddles in architectural history.
The committee stood down in 2001, but last year saw two intriguing postscripts to their work: first, the official announcement that the tower has been fully stabilised, its lean finally checked; and second, the publication of The Tower Restored, an intriguing 1,000-page account, co-authored by the whole committee, of every step they took to save the marble cylinder.
The original minutes of their meetings were never made public, prompting two decades’ accusations of gross incompetence and dodgy deals, most memorably after September 1995 when their interventions left the tower on the very brink of collapse. This tome is the committee’s comprehensive, if belated, reply. And it has stirred local feelings all over again.
Although now a quiet university town, back in its 12th-century pomp, fresh from naval victory over the Saracens of Sicily, Pisa was the pre-eminent maritime republic in Italy. To celebrate, the city elders built a cathedral, plus accompanying baptistery and belfry, on an open site in the city centre.
These early Romanesque masterpieces remain perhaps the finest trio of cathedral buildings on Earth, yet they could barely have been built in a less stable site – especially the 15,000-ton belfry (aka Leaning Tower) erected on just a 200sq m foundation.
Folly and genius went hand in hand, and visitors have been entranced ever since. Pisa lies on a thin layer of soft alluvial silt, above a thick layer of even softer marine clay. It’s practically a bog and only long breaks during the period of construction (1173 to 1370) - which allowed the underlying earth to compact itself and gradually adapt to the belfry’s weight - stopped it toppling over immediately.
The tower has tilted pretty much since day one and down the centuries proud Pisans have proclaimed only God was holding it up, out of love for their city. The name Piazza dei Miracoli seemed apt.
In the 19th century alone the tower crept southwards by a metre. Yet it wasn’t until the collapse of the San Marco belfry in Venice in 1902 that the authorities were roused in Pisa. Investigations were held throughout the 20th century – 16 different committees were appointed, of which Burland’s was the last – but nobody could work out what was causing the inclination. If the soil was uniformly unstable, why should the tower lean south rather than north?
Cue confusion, consternation and no end of wacky proposals, such as attaching helium balloons to the tower’s top, to hold it up; or re-landscaping the piazza, so it sloped in the same direction as the belfry leans, giving an optical illusion of everything being upright.
Mussolini, meanwhile, thought a wonky tower was a wholly unfit symbol for Fascist Italy and tried to restore its verticality, by drilling holes through the floor and pouring 80 tons of concrete into the foundations. As in so many things, though, Il Duce failed, and the tower continued its steady lurch, reaching 4.7m off-centre in 1989, the year yet another medieval belfry fell, the Civic Tower of Pavia (near Milan), killing four bystanders.
Pavia’s belfry was perfectly perpendicular, collapsing simply because of weakened, centuries-old masonry. It suddenly dawned on all in Pisa that their landmark could just as likely fall from structural failure as over-leaning. Indeed, the lean compounded stress on the first storey’s south side, the masonry of which was already starting to crack.
Enough was finally enough. In 1990, the Italian Prime Minister Giulio Andreotti closed the tower. ‘It was a brave move,’ Burland says, ‘because of all the various parties concerned.’ On a national level, two deadlocked government departments had been responsible for its safety, the Ministry of Cultural Heritage and the Ministry of Public Works, ‘who could never agree upon a positive course of action’; more locally, it had been run on a day-to-day basis by the Opera della Primaziale Pisana (OPP), an obscure vestry board that dates back to the Middle Ages.
Sidelining these parties, Andreotti assembled an independent, multidisciplinary committee (featuring 14 experts, from the fields of structural engineering, art history and architecture, plus geotechnical engineers like Burland). Handing over a £25m budget, he told them to hammer out a way of saving the tower forthwith, no matter how many late-night espressos it took.
Burland had helped save Big Ben from collapse during the Jubilee Line extension of the early Nineties, but progress in Pisa was far less smooth.
‘There were 14 egos at work and little common ground between people from such different disciplines,’ says Burland. ‘As opposed to rational, British-style discussion, meetings were emotional, with polemical speeches in Italian for hours on end. Often my translators struggled to keep up and I hadn’t a clue what was going on.’
Broadly speaking, the structural engineers disagreed with the geotechnical engineers over whether the key lay in the tower itself or in the earth beneath it, while both were at odds with the art historians, who feared intervention of any kind and demanded the belfry’s ‘character and integrity’ be observed. A permanent prop, for instance, was a definite no-no.
‘It was a constant impasse. I often doubted we’d ever reach a resolution,’ recalls Burland, one of only two non-Italians on the committee. The other, an American geotechnical engineer, died of a heart attack in 1996, partly brought on by the stresses of working in Pisa.
Members’ day jobs meant they met only once every six weeks. And initially they couldn’t even find a computer program that accepted a building tilting 4.7m could still be standing. What’s worse, the committee had been forbidden by Andreotti from making their discussions public, meaning their inactivity was pounced upon by a growing band of critics, who were forever kept in the dark.
Action was finally taken in 1992 (bracing the first storey with steel tendons, to relieve strain on its vulnerable masonry) and in 1993 (stacking 600 tons of lead ingots on the piazza to the tower’s north, to counterweight the lean). Yet both measures, especially the lead ingots, riled the aesthete Italian public, deforming as they did the slender tower’s bella figura.
In response, in 1995, the committee opted for 10 underground steel anchors, to invisibly yank the tower northwards. Little did they know, though, this would bring the tower closer to collapse than ever before, in an episode now known as Black September.
‘That was our darkest hour,’ Burland shudders. The anchors were to hang, 40m deep, from tensioned cables connected to the tower’s base. In view of Pisa’s high water-table, the committee froze the underlying ground with liquid nitrogen before any anchors were installed, to protect their excavations from flooding. The only trouble is, water expands when it freezes, so the shallow frozen groundwater pushed right up beneath the tower and then – once the freezing had stopped and the anchors were in place – created gaps in the soil for the tower to settle into.
On the night of September 7 1995, the tower lurched southwards by more than it had done in the entire previous year. Burland was summoned for an emergency committee meeting, and Ladbrokes were offering 11-4 odds the tower wouldn’t survive into the 21st century. ‘We really were within days of losing it,’ Burland says. The anchor plan was immediately abandoned and another 300 tons of lead ingots added.
The locals were up in arms, the Mayor of Pisa railing that a ‘plumber with a toilet-jack’ would have done a better job. Worse still, because they had to have their charter ratified every three months by the Italian parliament, Burland and co spent the end of 1995 and start of 1996, an election year, waiting for a new government to sanction them anew.
The lead eyesore remained, and several committee members’ cars were pelted with Tuscan tomatoes. Meanwhile, Pisa’s pre-eminent local historian, Piero Pierotti, cried foul. He maintains to this day that, up to Black September, measures were taken not chiefly to save the tower, but ‘to give jobs at highly remunerative rates’ to contractor cronies of certain Italian committee members.
The Tower Restored, however, offers a robust denial, the committee stressing they hit upon 1992’s steel tendons, 1993’s lead ingots and 1995’s anchored cables as purely temporary measures to avert structural collapse, until they found a long-term solution.
Burland was convinced he had such a solution – a process called soil extraction – and ultimately he won over the rest of the committee. Akin to microsurgery, it entailed drilling out slivers of soil from beneath the northern side of the tower - away from the lean - and allowing gravity to coax the structure back upright. It had the advantage of not touching the tower itself, so keeping the art historians happy.
‘The pressure was immense, a modern wonder of the world was at stake - but I never doubted the logic of soil extraction,’ says Burland, cool as you like. As revealed in The Tower Restored, the procedure was actually pioneered in 1832 by Victorian engineer James Trubshaw on the leaning church-tower of St Chad’s in Nantwich.
Work began in 1999, using delicate, Archimedes-screw drills. At the same time, technicians in a piazza-site trailer monitored data from 120 sensors set up inside and beneath the tower.
Burland now came into his own. He had details of the tower and earth’s every movement faxed twice a day to his office in London (or to wherever he was on holiday – the prof remembers one frantic search for a fax machine while away with his wife in Syria). And after considerable number-crunching, he would advise how much drilling was necessary in the next 12 hours. By the time he called a successful halt, two years and 1,500 faxes later, 70 tons of soil had been removed and the tower had returned to its early 19th-century inclination.
‘We could have removed more, but our aim was to make the tower safe with as little intervention as possible.’ Soil extraction brought the tower back by 50 centimetres to four metres off-centre – an amount that reduced the tilt and the stress on the vulnerable first storey enough to be safe, yet also maintained the distinctive lean.
Work officially stopped on June 17 2001, the feast day of San Ranieri, Pisa’s patron saint, greeted by a colourful parade of blaring trumpets and medieval costumes. The tower was due to reopen on September 12 but eventually did so in December; the original date deemed inauspicious just a day after the collapse of two other high-profile towers in New York.
‘It’s safe for another 200 years,’ the outgoing committee proclaimed, confident it would take two centuries for the tower to creep back to its tilt of 1999. Even then, engineers could repeat soil extraction without too much trouble and cut the inclination again. Part of the committee’s intention in writing The Tower Restored was to record their every action for posterity.
Yet, thanks to little-documented measures taken after the reopening, the tome shouldn’t need heavy consultation. Where soil extraction delayed a collapse by centuries, but never actually halted the leaning, Burland later oversaw a permanent solution, too.
Via his data analysis, Burland unlocked the 800-year mystery as to why the tower leans south not north: namely, a fluctuating water-table on the upper layer of silt. By a quirk of local geography, Pisa’s water-table rose higher on the tower’s north side, often reaching within one foot in rainy season, and this gave the tower an annual ratchet southward.
Armed with this vital information, in 2003, Burland introduced a new drainage system beneath the piazza’s north side, one that lowered and stabilised the water-table, so there’s no kick in either direction. Problem solved.
The inclination continues to be monitored daily by the OPP and new figures reveal that the tower didn’t move at all between 2003 and 2009. ‘It’s stopped leaning completely. After soil extraction and now the water-table stabilisation, the tower is safer than ever,’ says Burland with a mixture of pride and relief.
The Pisans, though, are a hard people to please. Some accuse Burland et al of sterilising their tower - for, part of its old mystique had been the possibility it might collapse at any moment, the frisson that a voyeuristic visitor might witness such a fall. ‘You can’t please all of the people all of the time,’ Burland shrugs.
He’s fascinated now by architectural advances in the UAE, where developers are striving to surpass each other with ever-taller, and ever-tiltier, buildings. Last month, the gravity-defying Capital Gate tower in Abu Dhabi – a giant, computer-concocted web of steel diagrids, which leans four times as far as Pisa’s belfry – entered the Guinness Book of Records as the world’s most inclined building.
‘It’s amazing that the Tower of Pisa should remain so fashionable, even at 800 years old,’ Burland smiles. Not bad for a building that was never meant to lean to begin with. ( telegraph.co.uk )
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