The Piazza del Duomo, also known as the Piazza dei Miracoli (Square of Miracles) is a large walled area in the heart of the city of Pisa. It is dominated by four great religious edifices: the Baptistry, Duomo, Campanile, and the Camposanto.In 1987 the whole area was declared a UNESCO World Heritage Site. The building of the Baptistery, opposite the west end of the Duomo, was begun in the mid 12th century. It was built in Romanesque style but the construction was not finished until the 14th century when the loggia, the top storey and the dome were added in Gothic style by Nicola and Giovanni Pisano At the heart of the Piazza is the Duomo. Construction was begun in 1064 by the architect Busketo in the distinctive Pisan Romanesque style of architecture. The façade of grey marble and white stone set with discs of coloured marble was built by a master named Rainaldo. The magnificent bronze main doors were made in the workshops of Giambologna. The campanile, the famous 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. The tower stands about 60m high, and was built to house seven main bells, cast to the musical scale. The tower is open to visitors who have a climb of 296 steps to the top!