Italy of the 15th century, and the city of Florence in particular, was home to the Renaissance. It is in Florence that the new architectural style had its beginning, not slowly evolving in the way that Gothic grew out of Romanesque, but consciously brought to being by particular architects who sought to revive the order of a past "Golden Age". The scholarly approach to the architecture of the ancient coincided with the general revival of learning. A number of factors were influential in bringing this about.
Italian architects had always preferred forms that were clearly defined and structural members that expressed their purpose. Many Tuscan Romanesque buildings demonstrate these characteristics, as seen in the Florence Bapistry and Pisa Cathedral.
Italy had never fully adopted the Gothic style of architecture. Apart from the Cathedral of Milan, largely the work of German builders, few Italian churches show the emphasis on vertically, the clustered shafts, ornate tracery and complex ribbed vaulting that characterise Gothic in other parts of Europe.
The presence, particularly in Rome, of ancient architectural remains showing the ordered Classical style provided an inspiration to artists at a time when philosophy was also turning towards the Classical.
Source: http://en.wikipedia.org/wiki/Culture_of_Italy#Renaissance_architecture
