The Piazza dei Miracoli (Italian: Square of Miracles), formally known as Piazza del Duomo (Italian: Cathedral Square), is a wide walled area located in Pisa, Tuscany, Italy, recognized as an important center of European medieval art and one of the finest architectural complexes in the world.Considered a sacred area by its owner, the Catholic Church, the square is dominated by four great religious edifices: the Pisa Cathedral, the Pisa Baptistry, the Leaning Tower of Pisa, and the Camposanto Monumentale (Monumental Cemetery). Partly paved and partly grassed, the Piazza dei Miracoli is also the site of the Ospedale Nuovo di Santo Spirito (New Hospital of the Holy Spirit), which houses the Sinopias Museum (Italian: Museo delle Sinopie), and the Cathedral Museum (Italian: Museo dell’Opera del Duomo).
The name Piazza dei Miracoli was created by the Italian writer and poet Gabriele d’Annunzio who, in his novel Forse che sì forse che no (1910), described the square as the “prato dei Miracoli” or the “meadow of miracles”. The square is sometimes called the Campo dei Miracoli (Field of Miracles). In 1987 the whole square was declared a UNESCO World Heritage Site.
The bell tower, commonly known as the Leaning Tower of Pisa, is located behind the cathedral. The last of the three major buildings on the piazza to be built, construction of the bell tower began in 1173 and took place in three stages over the course of 177 years, with the bell-chamber only added in 1372. Five years after construction began, when the building had reached the third floor level, the weak subsoil and poor foundation led to the building sinking on its south side. The building was left for a century, which allowed the subsoil to stabilise itself and prevented the building from collapsing. In 1272, to adjust the lean of the building, when construction resumed, the upper floors were built with one side taller than the other. The seventh and final floor was added in 1319. By the time the building was completed, the lean was approximately 1 degree, or 80 cm (2.5 feet) from vertical. At its greatest, measured prior to 1990, the lean measured approximately 5.5 degrees. As of 2010, the lean was reduced to approximately 4 degrees.
The tower stands approximately 60 m high, and was built to accommodate a total of seven main bells, cast to the musical scale:
L’Assunta, cast in 1654 by Giovanni Pietro Orlandi, weight 3,620 kg (7,981 lb)
Il Crocifisso, cast in 1572 by Vincenzo Possenti, weight 2,462 kg (5,428 lb)
San Ranieri, cast in 1719–21 by Giovanni Andrea Moreni, weight 1,448 kg (3,192 lb)
La Terza, the first small bell, cast in 1473, weight 300 kg (661 lb)
La Pasquereccia or La Giustizia, cast in 1262 by Lotteringo, weight 1,014 kg (2,235 lb)
Il Vespruccio, the second small bell, cast in the 14th century and again in 1501 by Nicola di Jacopo, weight 1,000 kg (2,205 lb)
Dal Pozzo, cast in 1606 and again in 2004, weight 652 kg (1,437 lb)
There are 296 steps leading to the top of the tower.