Now that is a name to conjure with but this Welsh, presumably prehistoric stone, found in the entrance porch of Corwen Church looks as weird as its name that it acquired over time. It is known in Welsh as 'Carreg y big yn y fach rhewllyd'.
Delving into the history of the church and we find that the two saints that it is named after, Mael and Sulien are early 6th century saints coming from Brittany. Corwen itself being an important Roman crossroad coming from London to Holyhead.
There is not much information on Mael but Sulien with his cousin Cadfan settled at Bardsey Island. There are many dedications to Sulien across Wales, from the Gower coast to Wrexham, sometimes his name being spelt Silian, and like all good saints his cult is strong in Brittany and Cornwall.. There is a well Ffynnon Sulien about a mile away the church, and other prehistoric sites.
Interestingly a fair was held on May 13th Ffynnon Fael, and at Llansilin in Denbighshire on October 1st, up until the 19th century, the last tuft of corn cut, the 'harvest mare' was mixed with the seed corn for the following year 'to teach it to grow'. The ashes from the 'yule log' were also used mixed with the 'mare' and 'seed', the harvest mare evolving into the corn dolly we see today. So says Breverton though it would be interesting to read other versions of how the corn-dolly came into existence, though less of the romanticised versions we find in the latest tranche of 'mystical' books.
Why was the stone built into the wall is the question, my theory is that it was such a scary stone that no one dared pull it out of the ground, but of course it could also point to the fact that with other prehistoric sites in the vicinity and it being an important Roman road junction, our two saints could easily have founded their church on an old 'pagan' site in their terminology, there would probably also have been a roman pagan shrine somewhere in the vicinity as well.
ref; The Book of Welsh Saints - T.D.Breverton
Another stone with a rather pointed top comes from Glandwr's churchyard, this having Ogam cut on its side. The stone found in the church yard, or probably chapel, maybe has links with the Via Julia that seems to be found round here according to the map.....
Note; Via Julia Montana - from Caerlon to Carmathen