John, Earl of Roxburghe (1680–1741) played a role in securing the Union of England and Scotland in 1707, and was rewarded by being created Duke of Roxburghe.
He commissioned the Scottish architect William Adam (1689–1748), father of Robert Adam, to design a new mansion incorporating the earlier tower house.
It was built between 1721 and 1726, and comprised a plain block, with towers at each corner.
Pavilions on either side housed stables and kitchens.

Around 1837, the 6th Duke (1816–1879) commissioned the fashionable architect William Playfair to remodel and rebuild the plain Georgian mansion house he had inherited.
The present form of the building is the result of Playfair's work, and is in a similar style to his buildings at Donaldson's College, Edinburgh.
In 1903, Duke Henry married the American heiress Mary Goelet.
She brought with her from her Long Island home a set of Gobelins Manufactory tapestries, that were incorporated into the ballroom in the 1930s, and added to the collection several modern pictures by Walter Sickert and Henri Matisse, among others.
John, Earl of Roxburghe (1680–1741) played a role in securing the Union of England and Scotland in 1707, and was rewarded by being created Duke of Roxburghe. He commissioned the Scottish architect William Adam (1689–1748), father of Robert Adam, to design a new mansion incorporating the earlier tower house. It was built between 1721 and 1726, and comprised a plain block, with towers at each corner. Pavilions on either side housed stables and kitchens.
Around 1837, the 6th Duke (1816–1879) commissioned the fashionable architect William Playfair to remodel and rebuild the plain Georgian mansion house he had inherited. The present form of the building is the result of Playfair's work, and is in a similar style to his buildings at Donaldson's College, Edinburgh. In 1903, Duke Henry married the American heiress Mary Goelet. She brought with her from her Long Island home a set of Gobelins Manufactory tapestries, that were incorporated into the ballroom in the 1930s, and added to the collection several modern pictures by Walter Sickert and Henri Matisse, among others.
Floors Castle