[A] curiosity in [Old Radnor] church [is] the extraordinary font, of the date of which it is impossible to form any opinion beyond the fact of its being a very early one, from the enormous dimensions of the bowl. It stands upon four clumsy feet, the under portion of the original mass having been cut away, leaving these rude supports.
The material is of a hard porphyritic rock, unlike any stone known in the vicinity, but said to be identical as to its character with the stones below in the valley, known as the Four Stones; so that if this is the fact, it is probable that it has been removed at some very early period from this so-called Druidic group, and converted to Christian use.
It's so easy to get confused when you're not a geologist. But if you are.. get down to the church immediately! Whatever the truth, it's a nice romantic thought. And ties in nicely with other speculation about the church.
from p366 of Archaeologia Cambrensis, v9 (third series), 1863.
Here's a picture of it, at 'Gathering the Jewels'. It really does have some resemblance to the squat Four Stones? but it is weird anyway, and seriously old if it really is 8th century as GTJ suggests (much older than the church). http://www.gtj.org.uk/item.php?lang=en&id=24339&t=1
I also spotted this intriguing stoney snippet in the Gentleman's Magazine (p514 in the Jul-Dec v11 for 1861):
..it was still a saying in Wales, "I would gladly carry a stone to his grave,"* and at Radnor it was, until very lately, the custom for mourners to carry a stone, which they cast down outside the churchyard.