IN THE OLD CHURCH OF KIRKMADRINE in Wigtownshire, and in the safe keeping of H.M. Ministry of Works, there are three inscribed burial stones. They are often described as "the Monogram  Stones of Kirkmadrine," and are remarkable for their age and style of sculpture. If the antiquaries are right, they were erected there about A.D. 450, and are the earliest inscribed Christian gravestones in Scotland. They mark the common grave and give the names of three priests. They were set up long before Scotland became a kingdom and they remained undisturbed through the political storms and religious changes of fourteen hundred years. About 1850 they were taken up and moved away. The two taller stones became the gate posts of the churchyard, and continued in that service for forty years. The third stone disappeared, and became known as "the lost stone of Kirkmadrine". This long lost and yet well known stone was found at last in 1916. It may be of interest to learn something of the strange eventful history of these three old and unique burial stones, and of the part taken in their recovery by the learned antiquaries of Edinburgh and by three men in the Rhinns of Galloway.

http://www.electricscotland.com/history/literat/kirkmadrine.htm