Vitruvius famously opened the first treatise on architecture with the statement that architecture requires the interaction between practice (fabrica) and reasoning (ratio). The former takes its form in buildings, the latter in treatises. Now that the practice of traditional and classical architecture and urbanism has been firmly reestablished, it is time to take another look at the complement to practice. Two treatises have dominated theory. Vitruvius, writing in the first century A.D., wrote the first one.¹ Leon Battista Alberti revised and reformulated that body of theory in the early years of antiquity’s restoration and renewal at the dawn of the modern age.² Together these two treatises present a comprehensive and rigorous theoretical complement to a rich and maturing practice in architecture. We know a little about the role of Vitruvius’ treatise before Alberti wrote his, and we know a great deal about the role they both played afterwards. To remain current they needed only fragmentary contributions or partial and respectful amendment to absorb new knowledge or to give theory a different emphasis…