Pisa is known worldwide for its Leaning Tower (the bell tower of the city's cathedral) and for the Miracle Square, a beautiful complex of Romanesque Architecture. The town is also home of the University, which has a history going back to the 13th century. The power of Pisa, as a mighty maritime nation, began to grow and reached its apex in the 11th century when it acquired traditional fame as one of the four main historical Maritime Republics of Italy. At that time, the city was a very important commercial centre and controlled a significant Mediterranean merchant fleet and navy .Pisa was the birthplace of the important physicist Galileo Galilei.