A stone upon the farm of Garreglwyd (formerly Tyn yr wtra) standing at the point of junction of the parishes of Aberhafesp, Tregynon and Bettws Ceewen. It bears an inscription which has been supposed to be of early date but the letters are modern, and doubtless stand for the initials of the churchwardens of the three parishes which have been inscribed upon what is probably an ancient boundary stone, in commemoration of an otherwise unrecorded perambulation of parochial bounds.
This is from 'An inventory of the ancient and historical monuments of the county of Montgomery' by the Royal Commission on the Ancient and Historical Monuments and Constructions in Wales and Monmouthshire (1911).
Today's Coflein record says the stone is quite small, only 1.1m high. But it concedes that 'the weathered condition of the stone may indicate reuse of an earlier monument'. So maybe it can still be Properly Old. So if anyone's passing and wants to take a photo..
There's a drawing and article here
in the Collections Historical & Archaeological Relating to Montgomeryshire.