Wonder No 7

Wonder No. 7

Leaning Tower of Pisa

• The Tower of Pisa is the bell tower of the Cathedral. Its construction began in the august of 1173 and continued (with two long interruptions) for about two hundred years, in full fidelity to the original project, whose architect is still uncertain. • In the past it was widely believed that the inclination of the Tower was part of the project ever since its beginning, but now we know that it is not so. The Tower was designed to be "vertical" (and even if it did not lean it would still be one of the most remarkable bell towers in Europe), and started to incline during its construction. • Both because of its inclination, and its beauty, from 1173 up to the present the Tower has been the object of very special attention. During its construction efforts were made to halt the incipient inclination through the use of special construction devices; later colums and other damaged parts were substituted in more than one occasion; today, interventions are being carried out within the sub-soil in order to significantly reduce the inclination and to make sure that Tower will have a long life. • The construction begun in 1173 and it must have been suspended at the completion of the third ring, around ten years later, since a subsidence of the soil of between 30 and 40 cm. had thrown the tower out of the perpendicular, causing an initial overhang of circa 5 cm. More than a century after the laying of the foundation stone, was once again begun (1275) by Giovanni di Simone, who added three more levels, correcting the axis of the Campanile. • In 1284 the six stories of loggias were to all effects finished, bringing the height of the building to 48 m., and employing a technical expedient that was meant to diminish, at least optically, the effects of the inclination, accomplished by raising the galleries of the upper floors on that side. • At the time the inclination of the Tower was more than 90 cm. The tormented vicissitudes of the Tower did not, as one might expect, greatly worry those who were involved in the construction and completion. The long intervals between building activity were dictated, most likely, by the need of letting the Campanile 'rest', but above all by letting both the foundations and the ground on which they rested settle down. • In a certain sense it can be said that the subsidence of the soil and the consequent inclination had, on the whole, been foreseen. At the beginning of the 14th century the bells were placed at the sixth level, in the large opening still visible in the marble cylinder beyond the loggia. Between 1350 and 1372 Tommaso di Andrea Pisano (according to Vasari) terminated the installation of the belfry on the summit of the sixth order of loggias, increasing the correction of the axis, and thus diminishing the load on the side that was in inclination, which in the mean while had become fixed at 1.43 m. • Conceived of not only as a bell tower, but also as a belvedere for the square below - from the earliest times the loggias have served as 'grandstand' for religious events and fairs - it rises 58.36 m above the level of the foundation, just under 56 m over the level of the countryside, and its inclination, measured at the base, is over 4 m. The average subsidence of the base is 2.25 m, while the progressio of the overhang, despite all attempts so far made to bring it to a halt, is about 1.2 mm per year.