Over the past four decades, the art collection at Russborough House has drawn both the attention of I.R.A. thieves and the interest of more than a million visitors to this 18th-century Georgian mansion.

Soon that collection will be smaller, though, thanks to a decision by the foundation that oversees the house to sell off nine artworks, including six old master paintings by the likes of Rubens, David Teniers the Younger and Francesco Guardi, at Christie’s in London next month.