The "Tristan Stone," for those not familiar with it, is an inscribed granite grave marker with a now only semi-legible text, probably dating to the sixth century, which stands just outside the Cornish village of Fowey. It is thought, by a group of Arthurian scholars, to provide evidence for the historical reality of Tristan, who was supposedly the son of the semi-legendary King Mark of Cornwall; this view, in my opinion, is very hard to sustain.
I wrote about the stone in some detail here, as part of a more extensive investigation of an early Breton ruler known as Conomor the Cursed, and as my discussion pretty much exactly answers your question, I am pasting it below.
The tl;dr is that the stone is currently sited about two miles from the spot where it is originally supposed to have stood, and has been at that site only since 1971; the exact spot where it originally stood is not known, so there have been no excavations around the monument itself, but it is sometimes thought to be associated with Castle Dore, an old hill fort sometimes thought to be the site of an important Cornish power locus of the period, and that site has been the subject of some archaeological research.
The various illustrations referred to in the text can be seen by clicking on the link above.
Anyone searching for the historical Conomor online will soon encounter references to an ancient monument in Cornwall which not only seems to refer to him, and provide additional evidence for the existence of a powerful British ruler who controlled territories on both sides of the Channel during the sixth century, but which has also been linked directly to the tale of Tristan and Yseult. It has been claimed that this “Tristan Stone” is proof that these two legendary characters were real historical personages, and that Tristan was the son of a King Mark, who was also known as Conomor, and who ruled from an important hill-fort, Castle Dore, which can still be seen a mile or two to the north of the spot where the monument now stands.
Today the “Tristan Stone” is to be found alongside the B3415, just outside the little port of Fowey, on Cornwall’s south-east coast – although the evidence suggests that it was originally erected some way to the north. The stone bears an inscription, now almost entirely worn away, which can be dated by its form and lettering to around the sixth century, and which (at least in the internet consensus) originally read Drvstanvs hic iacit filivs Cvnomoriv cvm domina Clvsilla. This can be – and has been – rendered, with the help of a considerable degree of favourable “interpretation,” as “Here lies Tristan, son of Conomor, with his lady Yseult.”
We’ll return to this interpretation in a moment. But let’s look first at what we know about the stone, its location and its history. What follows, I should note, is drawn from the major academic studies of such stones – those of Macalister and Okasha. I’ll deal with the rival, more ambitious claims of the archaeologist Raleigh Radford and the Arthurian scholar André de Mandach later.
The first thing to say is that, while the stone is estimated to be roughly 1,500 years old, records of its existence date back only as far as the sixteenth century writings of the Cambridge scholar John Leland, librarian and antiquarian to Henry VIII. Leland is of interest to us here because he travelled throughout England and Wales during the years c.1538-43 in order to compile an Itinerary of places, monuments and artefacts; he was in Cornwall in 1542, where he set down the earliest known description of what appears to be the “Tristan Stone.” His work, which was never published in his lifetime, exists today as an original manuscript in the Bodleian Library, Oxford. It was first published, in nine volumes edited by Thomas Hearne, in 1744-45 [vol.III p.26]; between 1907 and 1910, Lucy Toulmin Smith produced a scholarly edition of the work, and the passage that concerns us features here in the first volume (part III p.207): “Casteldour is longgid to [belongs to] the Erle of Saresbyri [Earl of Salisbury]. A mile of [off] is a broken Crosse inscribed: Conomor & filius cum Domina Clusilla.”
The second thing to point out is that the stone has moved – and, apparently, fragmented – in the time since Leland implied he saw it. If it was one mile from Castle Dore in 1540, then it was a full two and a half from Fowey, and Okasha summarises its subsequent movements as follows: it was relocated, probably before 1602, to a spot about a mile and a half away, on the roadside one mile from Fowey; by 1742 it had been dumped in a ditch along the Castledore road near Newton, where it was soon “half-buried” in accumulated muck; it was set upright once more about 1803, at the same spot; it was moved again, shortly before 1894, to “the centre of the highway outside Menabilly Lodge gates”; and in 1971 it was shifted yet again, slightly to the south, and re-erected at the place where it can now be found.
This is a history that combines periods of rough care with longer stretches of utter lack of care, and it is not very surprising that the inscription on the stone has become far less readable than it was when Leland apparently saw it. The wording itself is now in two lines, reading downwards and facing left. (Leland’s interpretation may imply there were once three.) It is in Latin, in capital script, and – thanks to its murky, deteriorated condition – it has been read rather differently by the various people who have seen it. The versions that have been published along the way include those of William Camden, in his Britannia of 1586; of the Welsh antiquary Edward Lhwyd (a friend of Isaac Newton’s who was Keeper of the Ashmolean Museum at the University of Oxford and a noted student of the Cornish language), in a private letter of 1700; of the Cornishman William Borlase, in his Antiquities of Cornwall, 1754; and of Daniel and Samuel Lysons, in the third volume of their Magna Britannia, 1814.
Listing these various interpretations in order of date, we have [with a slash, “/”, denoting a break between the lines, “-” an illegible character, ” and “{x}” a special character (in the case of the “Tristan Stone,” these are inverted letters – the letter ‘w’ being apparently represented, though it did not actually come into use until about 1100). The single exception here is the argument of John Rhys, Raleigh Radford and André de Mandach that the first letters, “Cl” should actually be read as a “D” carved in unical script)]:
CONOMOR & FILIUS CUM DOMINA CLUSILLA [Leland, 1542]
CIRVIVS HIC IACET / CVNOWORIS FILIVS [Camden, 1586]
CIRUSIUS HIC JACIT / CUNOWORI FILIUS [Lhwyd, 1700]
CIRVSIVS HIC IACIT / CVNOWORI FILIVS [Borlase, 1754]
CIRUSIUS HIC JACET / CUNOWORI FILIUS [Lysons, 1814]
DRUSTAGNI HIC IACIT CVNOWORI FILIVS [Rhys, 1875]
CIRVSINIVSHICIACIT / CVNO{M}ORIFILIVS [Macalister, 1945]
[CIRV–V–NCIACIT] / CV[N]O[{M}]ORFILVS [Okasha, 1985]
{D}RVSTA/NVSHICIACIT / CVNO{M}ORIFILIVS [Thomas, 1994]