Horace Walpole & Landscape Gardening (pg 13)

Horace Walpole (1717-1797), also known as Horatio Walpole, was the 4th Earl of Orford and a reasonably successful English politician and writer. He is well known for helping to revive an interest in the Gothic style in the Victorian Age. His contributions to the Gothic revival were literary and architectural.  He wrote a successful Gothic novel, The Castle of Otranto, which he published under a
pseudonym, and built a prominent Gothic estate named Strawberry Hill at Twickenham outside of London. Strawberry Hill is considered one of the earliest examples of Gothic revival estates. It features towers, battlements, vaulted arches, and vaulted windows in an effort to simulate the elaborate styles and gloomy essence of medieval Gothic construction. This Gothic style was also emulated in Victorian landscape gardening, with fake Roman and medieval ruins (often called "follies"), hermitages, and other exotic buildings becoming fixtures of Victorian gardens and status symbols for wealthy families.

The mention of Horace Walpole in Arcadia is important because it explains the inspiration behind Lady Croom's elaborate garden renovations, which seem to be important for the setting and plot motivation, while giving us some insight into the characters. The fact that Lady Croom is unaware of the connection between The Castle of Otranto and Horace Walpole suggests that she is only shallowly concerned with participating in the Gothic-revival trend and not aware of its foundations. This ignorance could possibly foreshadow other misunderstandings/miscommunications and have an effect on the Sidley Park research of Hannah Jarvis and Bernard Nightingale later in the play.

Sources:

http://en.wikipedia.org/wiki/Strawberry_Hill_House
http://en.wikipedia.org/wiki/Horace_Walpole
http://en.wikipedia.org/wiki/English_landscape_garden