The Syon estate was first established when a Bridgettine monastery founded by Henry V erected a quadrangular building there in 1431. Most of the fabric of this original building was lost owing to extensive rebuilding works to convert it into a house, conducted by Lord Protector Somerset from 1547, although the monastic quadrangle continues to dictate the footprint of the building. The Percy family acquired Syon in 1604 when the estate was granted to the 9th Earl of Northumberland by James I. Extensive Jacobean style repairs and alterations were commissioned by the 10th Earl in 1665-70 to designs by John Webb (1611-72), but little of this work survives owing the eighteenth-century additions by Robert Adam.

Hugh Smithson (1712-86), succeeded his father, Sir Langdale Smithson, as the 4th Baronet in 1727, aged 17. The Smithson family had made a fortune in haberdashery on Cheapside, and bought the Stanwick estate near Catterick in 1638. The 1st Baronet had been created by Charles II in 1663 because he had supported Charles I during the Civil War. Smithson went on to inherit estates and wealth from his sister and cousin, and in 1740 he married Lady Elizabeth Percy (d1776), the daughter of the 7th Duke of Somerset (her maternal grandfather was the 11th Earl of Northumberland). As Elizabeth’s only sibling, George, died of smallpox during his Grand Tour in 1744, she inherited everything in 1750 from both the Dukedom of Somerset, and the Earldom of Northumberland. This not only brought Sir Hugh the estates of Syon, Alnwick Castle and Northumberland House on the Strand, but also the Earldom, elevating him to 12th Earl of Northumberland.

In 1766 the Earl was created 1st Duke of Northumberland (third creation of the dukedom of Northumberland). His incredible rise was partly thanks to his marriage, partly thanks to a friendship with Lord Bute (his son married Bute's daughter in 1764), and partly thanks to his various public offices. He had served as MP for Middlesex in 1740-50, until his elevation to the Earldom when he became active in the House of Lords. He was also Sheriff of Yorkshire in 1738-39; a trustee of the British Museum in 1753-86; a Lord of the Bedchamber in 1753-63; Lord Lieutenant of Northumberland in 1753-86; Lord Lieutenant of Middlesex in 1763-65; Vice-Admiral of North America in 1764; and Master of the Horse in 1778-80. Moreover, he was a skilled land manager, exploiting coal reserves, and vastly increasing the financial yields of his estates, and enabling him to undertake large-scale rebuilding works across the country. By these means, Northumberland became one of the greatest patrons of the arts, and his Duchess was a renowned connoisseur, undertaking numerous tours of other great country houses, in an effort to observe and record the works undertaken by her contemporaries.

In 1761 Northumberland cast aside his previous architect, James Paine, and commissioned Robert Adam to make designs for a suite of rooms on the principal (ground) storey at Syon, to replace the Jacobean rooms installed by his wife’s great-grandfather, the 10th Earl. Adam's work included rooms within all four ranges of the quadrangular house, as well as a large circular saloon within the 80 foot square central courtyard - former cloisters - which was not executed, but is now mapped out with box hedging. There is no surviving plan showing Adam's scheme, but it is illustrated in a plan in The works in architecture of Robert and James Adam (part I, plate v). Adam executed rooms within three of the four ranges, as well as a bridge and gate with lodges, but the central circular saloon was not built, save for a temporary structure, probably of wood and canvas, erected for an entertainment in honour of the King of Denmark in 1768. This entertainment was recorded by Mrs Delany. Although his works within the interior of the house were extensive, Adam hardly touched the exterior, with the exception of installing slightly wider window sash bars than had been used previously.

Much of Adam's work at Syon is in his early style, and the hall and dining room ceilings are particularly heavy. The plasterwork was carried out by Joseph Rose, the carving by Sefferin Alken and John Adair, and there is furniture in the house by John Linnell, Thomas Chippendale and William France. Adam also made alterations to Syon Lodge, the dower house on the estate. There are no surviving drawings for this work, and the building was sold in 2007. It is now privately owned.

Adam's interiors at Syon remain remarkably well preserved considering there have been various alterations made to the house since the 1760s. In 1789-90 James Wyatt (1746-1813) added stables and an iron bridge within the park for the 2nd Duke. And in the 1820s the 3rd Duke commissioned the large glass conservatory to the north of the house to designs by Charles Fowler (1792-1867), and works to the house itself to the designs of Thomas Cundy senior (1765-1825), including new decoration within the north range (the range in which there was no Adam interior decorative work), and the re-facing of the exterior in Bath stone. Syon remains in the ownership of the Dukes of Northumberland, being the largest suburban London mansion still in private ownership, and is open to the public.

There are further Adam drawings for Syon at the V&A Museum, which comprise designs for the porter’s lodge and the gallery, and there are numerous engravings of Adam’s works at Syon in all three volumes of The works in architecture of Robert and James Adam. Syon is the most heavily represented of Adam's works within the publication.

See also Northumberland House and Alnwick Castle

Literature:
R. Adam, The works of Robert and James Adam, 1773-78, 1779, 1822, Volume I, part I, plates i-viii, Volume II, part IV, plates i-viii, Volume III, plates ii-ix; A.T. Bolton, The architecture of Robert and James Adam, 1922, Volume I, chapter xiv, Volume II, index p. 28; J. Lees-Milne, The age of Adam, 1947, pp. 107-111; E. Harris The furniture of Robert Adam, 1963, Index p. 52, pp. 66-68, 77; D. Stillman, The decorative work of Robert Adam, 1966, pp. 19, 28, 32, 37, 46, 48, 63-65, 67, 80, 97, 98, 107; D. Yarwood, Robert Adam, 1970, pp. 118-122, 137, 199-200; G. Beard, The work of Robert Adam, 1978, pp. 10-11, 43-44, 58-59; H. Hayward, and P. Kirkham, William and John Linnell: eighteenth-century London furniture masters, 1980, pp. 120-23; B. Allen, ‘Joseph Wilton, Francis Hayman and the Chimney-Pieces from Northumberland House’, Burlington Magazine, Vol. 125, No. 961, April 1983, p. 199; A. Rowan, Catalogues of architectural drawings in the Victoria and Albert Museum: Robert Adam, 1988, p. 85; B. Cherry, and N. Pevsner, The buildings of England: London 3: North West, 1991, pp. 442-45; E. Harris, The genius of Robert Adam: his interiors, 2001, chapter 4; D. King, The complete works of Robert & James Adam and unbuilt Adam, 2001, Volume I, pp. 12-13, 22, 25, 184, 225, 232-37, 355-56, 368, 397, 401-2, Volume II, pp. 204-7, 225; E. Harris, The country houses of Robert Adam from the archives of Country Life, 2007, pp. 54-65; Oxford dictionary of national biography online: ‘Percy [formerly Smithson], Hugh, first duke of Northumberland (ba. 1712, d. 1786)’

Frances Sands, 2013