Long before anyone thought of building trophy houses, one man changed forever the concept of how high, given the money, the standards should be. Five hundred years after the birth of Andrea Palladio, Gully Wells explores his work in a corner of Italy endowed with a cluster of masterpieces

In 1792, Thomas Jefferson drew up plans for a new President's House in Washington, D.C. The design, like its architect, was elegant and innovative: a perfect cube, with four identical porticoes surrounding a circular domed rotonda. But—as so often happens in Washington, then as now—originality and brilliance were regarded with some suspicion, and the place Jefferson moved into nine years later was not the one he had designed. However, he never forgot his dream house, and once he'd finished with the presidency, he resurrected the blueprint and it became the inspiration for Monticello and for the library at the University of Virginia, buildings that represent both the apotheosis of neoclassical beauty and Jefferson's architectural genius. But who was Jefferson's inspiration? Who would Jefferson have regarded as the real genius?

According to a letter written by a Colonel Isaac Coles, dated February 23, 1816: "With Mr. Jefferson I conversed at length on the subject of architecture. Palladio, he said, 'is the Bible. Stick close to it.' " Strong stuff, even from a moderately God-fearing man.

For a stonemason, born five hundred years ago in a small town in the Venetian Republic, Andrea Palladio's impact on Western architecture is of, well, biblical proportions. The British were the first to fall under Palladio's spell, and from there his style spread like pollen all over the ever expanding empire. In the thirteen colonies, from the capitol in Williamsburg, Virginia, to the pediment and pillars of a courthouse in New England, to the double porticoes of a plantation house (like Drayton Hall, in Charleston, South Carolina), the influence of the master was inescapable.

Palladio was a man of the Veneto—the Venetian mainland, known to the inhabitants of the lagoon as "terra firma" (although, it was not so firma at the time: The marshy land had to be drained before it could be used for agriculture and built upon). His villa commissions came from the local nobility as well as from patrician Venetian families eager to acquire a place in the country. The happy result, for the twenty-first-century traveler, at least, is that Palladio's masterworks (in all there are seventeen villas, three churches, and one theater) are clustered quite close together in and around Vicenza, Padua, Asolo, and of course Venice.

Poor Mr. Jefferson never actually saw a Palladian building; his knowledge and adoration were based upon Palladio's treatise, The Four Books of Architecture, published in Venice in 1570. Palladio's architectural principles were based upon his study of ancient Roman buildings (see graphic, below). Rome was Palladio's inspiration, but his true genius lay in his ability to adapt the monumental and public style of Roman architecture and make it work on a smaller, domestic scale.

For the modern-day Palladio aficionado, however, books are still the beginning of the journey, and so last spring I made a visit to the New York Public Library on Fifth Avenue (a flight of steps sweeps up to a massive portico, with its six pillars and pediment—an homage to you know who), and settled down with a pile of books, a detailed map of the Veneto, and a red pen, which I used to mark every single Palladian building and its location. After that, it was just a question of connecting the dots.