Leon Battista Alberti (1404-72) who was the first, consciously and completely, to carry out the new ideals. In his De re aedificatoria (1485) he defined what seemed to him to be the essential of architecture: 'The harmonious unity of every part, combined in such a way that nothing can be added, subtracted, or altered, that is not for the worse.' The facade of the Palazzo Rucellai in Florence (1446-51), with its perfect harmony and proportion, exemplifies this maxim; so do his churches, S. Andrea and S. Sebastiano at Mantua, S. Francesco at Rimini (usually known as the Tempio Malatestiana), and S. Maria Novella at Florence.
In the churches built by Alberti and other architects in the late fifteenth and very early sixteenth centuries, there is a frequent use of the Greek cross plan that is to say, a cross with equal arms, as opposed to a Latin cross in which one arm, the nave, is longer than the other three. This is another instance of the early Renaissance conception of space, with its ideals of clarity, lucidity and order, and its idea of a building as something as unified and harmoniously proportioned as a crystal.
Florence was the centre of the early Renaissance, but about the turn of the century the centre moved to Rome, where all the great architects of the High Renaissance, Donato Bramante, Raphael, Michelangelo and Peruzzi, none of them Roman by birth, gravitated.