The Piazza del Duomo ("Cathedral Square") is a wide, walled area at the heart of the city of Pisa, Tuscany, Italy, recognized as one of the main centers for medieval art in the world. Partly paved and partly grassed, it is dominated by four great religious edifices: the Duomo (cathedral), the Campanile (the cathedral's free standing bell tower), the Baptistry and the Camposanto.
It is otherwise known as Piazza dei Miracoli ("Square of Miracles"). This name was created by the Italian writer and poet Gabriele d'Annunzio who, in his novel Forse che si forse che no (1910) described the square in this way:
L’Ardea roteò nel cielo di Cristo, sul prato dei Miracoli.
which means: "The Ardea rotated over the sky of Christ, over the meadow of Miracles."
Often people tend to mistake the term with Campo dei Miracoli ("Field of Miracles"). This one is a fictional magical field in the book Pinocchio, where a gold coin seed will grow a money tree.
In 1987 the whole square was declared a UNESCO World Heritage Site.
The heart of the Piazza del Duomo is the Duomo, the medieval cathedral, entitled to Santa Maria Assunta (St. Mary of the Assumption). This is a five-naved cathedral with a three-naved transept. The church is known also as the Primatial, the archbishop of Pisa being a Primate since 1092.
The Baptistery, dedicated to St. John the Baptist, stands opposite the west end of the Duomo. The round Romanesque building was begun in the mid 12th century: 1153 Mense August fundata fuit haec ("In the month of August 1153 was set up here..."). It was built in Romanesque style by an architect known as Diotisalvi ("God Save You"), who worked also in the church of the Holy Sepulchre in the city. His name is mentioned on a pillar inside, as Diotosalvi magister. the construction was not, however, finished until the 14th century, when the loggia, the top storey and the dome were added in Gothic style by Nicola Pisano and Giovanni Pisano.
The campanile (bell tower) 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 2.5 feet (80 cm) from vertical. At its greatest, measured prior to 1990, the lean measured approximately 5.5 degrees. As of 2010, this has been reduced to approximately 4 degrees.