Trethevy (Cornish: Tredhewi)[1] is a hamlet in north Cornwall, England, United Kingdom.

[2] Roman occupation of Trethevy is suggested by an inscribed granite pillar, once used as a gatepost and now situated on the roadside by St. Piran's, a reputed former monastery and now a private residence.

The inscription on the stone reads C DOMI N GALLO ET VOLVS – 'For the Emperor Caesars our lords Gallus and Volusian.'

The "monastery" tradition is likely to be an elaboration of William Goard based on R. S. Hawker's reference to "the reliques of a cell".

For some 300 years the farmhouse of Trethevy was home to the family of Wade some of whom were mayors of the borough of Bossiney.

Sir John Maclean stated that Trethevy was at some time between the 16th and 19th centuries held by the family of Trefusis but without the date or other details.

A fourth part of the estate at Trethevy belonged to George Smith (died 1652), of Lantewy and Lunna in St Neot, who was succeeded by his daughters Mary and Katherine.

[5] In the late 19th and early 20th centuries, a series of villas were built along the east side of the lane leading to St Nectan's Glen.

[citation needed] The waterfall is a popular tourist destination and is viewed by some as a sacred site; at its base are many ribbons, photos, inscriptions, prayers and other offerings.

Further upstream from Saint Nectan's Glen were the remains of a longhouse, Tregenver, possibly as old as the fourteenth century.

[7] Charles Dickens and William Thackeray visited Saint Nectan's Glen in 1842 along with Daniel Maclise, who made his preliminary sketches for Nymph at the Waterfall here.