By the marriage between Lady Elizabeth Percy and Charles Seymour, Duke of Somerset, Sion House became the property of the latter, and during his ownership it was lent for a time to the Princess Anne, later Queen of England, who there gave birth to a son who lived for an hour only, one of her seventeen children, none of whom grew up. The son of Charles Seymour gave Sion House to his daughter Elizabeth in 1748, and her husband, Sir Hugh Smithson, having been created Duke of Northumberland, it passed back to the old earldom, and has ever since remained in the same family. It was the new duke who gave to the historic mansion the character that now distinguishes it, for he made considerable alterations and additions, entrusting the work to the then renowned architect, Robert Adam, who is said to have consulted Sir Horace Walpole, then living at Twickenham, on the subject of the internal decorations. The gardens, originally laid out by the Protector Somerset, and greatly improved by later owners, were still further enriched with rare plants; hothouses and conservatories were built, and the estate was converted into one of the most charming on the Thames, beautiful lawns, shaded by venerable trees, sloping down to the waterside. The massive quadrangular mansion, with a square tower at each corner, and a noble {284} parapet, the eastern front surmounted by the venerable stone lion, the badge of the Percy family, that was long a familiar figure on the Strand front of the now demolished Northumberland House, rises up in quiet dignity from the park which, though it has none of the varied scenery of its rival at Richmond, is full of quiet charm. [Sidenote: Marble Hill]