James Wyatt (1746–1813), a fashionable and extremely prolific[4] architect of the time, was commissioned to design a mausoleum to hold the coffins of the Earls and their family members.

The form is an unusually grand classical temple, using Roman Doric order, fluted columns in antis on the face, prostyle on the angles.

However, the pyramid-shaped roof, the mausoleum's most distinctive feature, while usual in classical architecture may have been derived by Wyatt from a painting by Nicolas Poussin rather than directly from antique precedents.

On the piano nobile, there is a circular chapel with Tivoli variant Corinthian order columns of rose marble and a coffered dome of stone.

[1] The mausoleum is important because of its architect, its situation in parkland at a predominant position on the North Downs, and as a demonstration of 'the Age of Enlightenment's preoccupation with a 'classical way of death'.

It continued to decline, and schemes proposed included moving it to Shorne Woods Country Park or the United States, or for major extensions to form a large classical house.

In 2013, on completion of the restoration of the mausoleum, it was transferred to the National Trust, along with the area of historic pasture and grazed woodland surrounding it.