Donyarth (Latin: Doniert) or Dungarth was the last recorded king of Cornwall, the rump state of the ancient British kingdom of Dumnonia, which had also covered Devon. He was probably an under-king, subject to the West Saxons.

History: In the fifth century, Christianity was first brought to Cornwall by monks from Wales and Ireland. The early missionaries are believed to have erected wooden crosses to show places in which they had won victories for Christ. In time, these places became sanctified and the wooden crosses were replaced by stone ones.

The Site: The site consists of the remains of two 9th-11th century granite cross-shaft fragments and an underground passage and cross shaped chamber below the crosses thought to be either the remains of tin workings or a possible oratory. The northern cross, termed the "Doniert Stone" is 1.37 metres high with panels of interlace decoration on three sides and inscription "doniert rogavit pro anima" carved in Insular script . The inscription translates as "Doniert has asked [for this to be made] for his soul(’s sake’)". The inscription is thought to refer to the local ruler "Dumgarth" (or "Dwingarth") who is recorded in the early Welsh chronicle known as the Annales Cambriae, as having drowned in around 875 AD (possibly whilst out hunting). His death may have been an accident, but it was recorded in Ireland as a punishment for collaboration with the Vikings, who were harrying the West Saxons and briefly occupied Exeter in 876 before being driven out by Alfred the Great. Philip Payton states that one must imagine that he drowned in the River Fowey, near King Doniert's Stone.

. It has a mortise slot and a plinth at the base.

The southern cross, sometimes referred to as the "Other Half Stone", is 2.1 metres high with a panel of interlace decoration on the east face, a broken mortise slot at the top and a plinth at the bottom.

Excavations: In 1849, the Exeter Diocesan Architectural Society carried out excavations around the stones and discovered a hidden vault beneath them. Mr Charles Spence published in the Transition of that Society a paper entitled ‘Iter Cornubiense’ in which he details the proceedings of the work. ‘After raising Doniert's stone and placing it in an erect position a mass of granite no less than two tons and a half in weight the workmen were directed to dig down by the side of the other monolith. ‘After reaching a depth of about eight or nine feet a hole was discovered. Here they found a cruciform vault eighteen feet in length from east to west and sixteen from north to south the width of the vault being about four feet. The sides were perpendicular and the roof circular and all smoothed with a tool and as level as the rough nature of the naked rock would permit.' The men employed for this task came from South Caradon mine. It was reported that the miners said that it was ‘nothing but old workings in other words ancient mine works.

The underground rock-cut chamber begins as a passage about 8 metres to the south east of the crosses, turns into a tunnel and ends as a cruciform chamber beneath the crosses. The relationship between the underground chamber and the crosses is unknown.

The site is managed by the Cornwall Heritage Trust on behalf of English Heritage. Vehicles can park in a layby adjoining the site, entry is free and the site can be visited at any reasonable time during daylight hours.