The direct impact of Palladio's text was upon building patrons,[2] for these expensive volumes were out of the reach of most builders, who could consult them only briefly in a gentleman's library.
In 1738 Isaac Ware, with the encouragement of Richard Boyle, 3rd Earl of Burlington, produced a more accurate translation of Palladio's work with illustrations which were faithful to the originals, but Leoni's changes and inaccuracies continued to influence Palladianism for generations.
Giacomo Leoni's principal architectural skill was to adapt Alberti's and Palladio's ideals to suit the landed classes in the English countryside, without straying too far from the principles of the great masters.
In the early 1720s, Leoni received one of his most important challenges: to transform a great Elizabethan house, Lyme Hall, into a Palladian palace.
[6] This he did so sympathetically that internally, large areas of the house remained completely unaltered, and the wood carvings by Grinling Gibbons were left intact.
However, it has been claimed that the central Ionic portico, the focal point of the south front, was a little spoiled later by English architect Lewis Wyatt's 19th-century addition of a box-like structure above its pediment.
Leoni reconstructed Lyme in an early form of what was to become known as the Palladian style, with the secondary, domestic and staff rooms on a rusticated ground floor, above which was a piano nobile, formally accessed by an exterior double staircase from the courtyard.
In a true Palladian house (one villa designed by Palladio himself), the central portion behind the portico would contain the principal rooms, while the lower flanking wings were domestic offices usually leading to terminating pavilions which would often be agricultural in use.
It was this adaption of the wings and pavilions into the body of the house that was to be a hallmark of the 18th-century Palladianism that spread across Europe, and of which Leoni was an early exponent.
[8] However, at this early stage of his career Leoni appears to have been still following the earlier and more renaissance-inspired Palladianism which had been imported to England in the 17th century by Inigo Jones.
This is evident by his use of classical pilasters throughout the south façade, in the same way that Jones had used them, a century earlier, at the Banqueting House, Whitehall and Leoni's mentor, Alberti, had employed them at the Palazzo Rucellai in the 1440s.
Clandon was built of a fiery red brick, with the west front dressed with stone pilasters and medallion ornamentation.
The interiors were altered slightly later in the 18th century, but here the house was fortunate; the changes were made in the style of Robert Adam, so were sympathetic to Leoni's original intentions.
Both were similar in concept to Andrea Palladio's never-built Villa Mocenigo, with great spreading and segmented colonnaded wings embracing a cour d'honneur.
The secondary wings or blocks, each crowned with a cupola, were similar in style to those built by Henry Flitcroft for the Duke of Bedford twenty years later at the far larger Woburn Abbey.
[19] Later, as Leoni lay dying in 1746, Lord Fitzwalter sent him a further £8 "par charité"[20] He is known to have had a wife, Mary, and two sons, one of whom is "thought" to have been a clerk to the great exponent of Palladianism Matthew Brettingham.
By the early 20th century, the style of Palladianism which Leoni's books and works did so much to promote,[22] was so quintessentially English that the fact that it was regarded as purely Italian at the time of its inception was largely forgotten.
So indigenous to England does it seem, that in 1913 – a time of huge pride in all things British – Sir Aston Webb's new principal façade at Buckingham Palace strongly resembled Leoni's 'Italian palazzo.'
His final intended publication, which would have added to an evaluation of his work "Treatise of Architecture and ye Art of Building Publick and Private Edifices—Containing Several Noblemen's Houses & Country Seats’ was to have been a book of his own designs and interpretations.