Palladio used a Vitruvian system: as the numbers six and ten were found to appear throughout the ratios of the body, he felt they would bring balance and understanding to rooms around us. He also felt that as 16 is the sum of six and ten, ratios involving it would also create balance. Any ratio involving these three numbers could be incorporated. In addition to being inspired by Vitruvius, Palladio also used musical ratios. People had been using the ratios of 1:2, 2:3 and 3:4 for eons. Palladio developed a more complex system of harmonic proportions based on the major and minor third, which result in the ratios 5:6 and 4:5.

Villa Cornaro, begun 1552	Villa Emo, begun 1559
(the initial model for Monticello)

Villa Cornaro demonstrates Palladio's use of the Vitruvian system in the dimensions of its rooms. The numbers 6 and 10 appear throughout Vitruvius' ratios of the body, so Palladio felt they would bring balance and understanding to the rooms around us. He also felt that 16, as the sum of 10 and 6, ratios involving it would also bring balance. Palladio felt that any ratio involving any pair of these three numbers would promote harmony. The ratio of the proportions in the upper rectangular rooms of this plan are three to five (which is the same as 6 to 10), with an actual measurement of sixteen Vicentine feet.

Villa Emo demonstrates his use of a harmonic system of proportion. Measuring the rooms of the central block in Vicentine feet, Palladio used a 27-foot square for the central hall, with additional rooms of 12 x 16, 12 x 27, 16 x 16, and 16 x 27 framing the hall and the portico (16 x 27). Meanwhile, various chambers in the wings include measures of 12, 24, and 48. Scholars such as Rudolf Wittkower have identified the numbers 12, 16, 24, 27, and 48 as the terms of musical harmonies.

Palladianism spread to England through British architect Inigo Jones in the 17th century. From England, it spread to the United States. Redwood Library, the oldest lending library in the United States, right in our backyard in Newport RI, was (according to their web page, at any rate) the first pure example of English Palladianism in the colonies.

The Redwood Library, completed in 1750, Newport Rhode Island

The Modulor