Italian architecture of the sixteenth century is a field where our knowledge has outdistanced our concepts. We are in firm possession of many facts, but we cannot agree as to how they should be interpreted. What is called for is a fresh conceptual framework into which the facts can be fitted. Such a framework cannot be derived from a simple contrast of the Renaissance and the Baroque, nor can it be made to depend on a single catch-all title like Mannerism. It must have three principle characteristics. It must be based on an aesthetic analysis of the monuments. It must include all the principle groups of buildings. Finally it must bear some reasonable relationship to the general view one holds of Italian sixteenth century history as a whole.