June 17, 2011 --
Today, on the day of its patron saint Ranieri, Pisa celebrates the free-standing Leaning Tower after 20 years of restoration work. Exactly 10 years ago, the tower re-opened for the first time since 1990, as work to keep it from collapsing was completed. The tower now leans only 4.1 meters (13.5 feet) off perpendicular, 44 centimeters (17 inches) less than it was before the restoration. However, scaffolding around Italy’s most iconic monument remained at the site for another decade. In 2002 restorers begun the towering task of removing centuries of grime and dust from more than 7,000 square meters (75,347 square feet) of marble.
Healthier than ever, the tower is also much whiter. According to those who worked on the restoration, led by Gisella Capponi, director of the Institute for Conservation and Restoration at the Ministry of Cultural Heritage, the condition of the marble was strongly influenced by the lean, which enhanced the decay process caused by the natural aging of the materials. In fact, signs of structural damage began to appear only a few years after the completion of the tower: Four columns had to be replaced already in at the end of the 14th century.
The soft, sandy subsoil is what has given the 179-foot tower its lean since Bonanno Pisano began building it in 1173. In fact, the tower first started to subside when it was only 30 feet high.
Construction on the Tower began in August 1173, and continued without interruption for five years. In 1178, the work was halted at the fourth story. One hundred years later, in 1272, construction work was resumed and in 1278 the tower reached the seventh level. After another long pause, in 1360 work on the bell chamber begun. The lean was clearly visible and workers tried to correct the angle by adding six steps on the south side, and only four steps on the north side. Pisa's most famous landmark was officially completed about 1370.
Over the years, the original components of the tower, mainly made of marble from the nearby village of San Giuliano, were gradually replaced with white Carrara marble. Today, only 33 of the 180 pillars of the open galleries are made of San Giuliano marble, and are located mostly on the northeastern side.
Scientific analysis and a complex mapping of the different forms of decay showed that the tower suffered from widespread cracks and fragmentation as a result of the compressive forces produced by the lean and the greater exposure to the sun's rays. In the wetter areas, restorers found micro-organism, mosses, lichen and weeds.
Black crust, mainly located on the lower colonnades of the south side covered 1,968 square meters (21,183 square feet) of marbles. Decay on the stone, affecting 2,086 square meters (22,453 square feet), was more severe in the upper areas of the north and south side. Cracks extended for 8,658 square meters (93,193 square feet) and were most pronounced at the third level.
To clean the tower, the restorers used various methods, which involved consolidating the marble, sealing cracks and cleaning the tower by using atomized water spray, solvent poultices or micromechanical tools. Special treatments were also used to remove chewing gum and graffiti.
The tower was saved from tumbling over after a decade-long engineering feat in the 1990s. The lean, which previously increased at a rate of one millimeter a year, was fixed with the simplest and most intuitive solution: by sinking the higher side. More than 40 drills were used to remove 20 cubic meters (706 cubic feet) of earth from the side away from the tilt. The tower -- 14,000 tons of intricately carved white marble -- was steadied by steel cables attached to the second tier and anchored to the ground. Some 800 tons of lead counterweights (seen here) were also placed on the side opposite the lean. The restoration has made the tower safe for the next 300 years.
No fewer than 17 committees have debated on how best to correct the monument's increasingly acute angle. The archives of the Opera Primaziale, the body responsible for the tower's care, are full of schemes proposed over the past 150 years. In this photo, a tourist poses beside the tower pretending to hold it up.
The Leaning Tower of Pisa may be the most famous tilted tower in the world, but a number of German villages are now fighting for the title of the world's most lopsided building. An East Frisian church tower in the village of Midlum boasts a record-topping angle of 6.74 degrees. However, the tower stands only 46 feet high, and its top deviates from a vertical position by only 5.2 feet. A crumbling medieval fortress tower in Dausenau, in the western Rhineland-Palatinate region, has now drifted 5.24 degrees from its original vertical position. Since the tower is ruined, is ineligible for the prized title. The winner seems to be the church of Suurhusen (seen here) in East Frisia, which won the "most leaning" status in the Guinness World Records in 2007 for its alarming drunken angle of 5.19 degrees. By comparison, the Leaning Tower of Pisa boasts a "small" 3.99-degree tilt.