Many theories have been advanced with respect to their origin. They are variously supposed to have been idol-stones, to have been erected as landmarks, and as monumental stones recording the scene of a battle, or the spot upon which a warrior had fallen. The name ‘cat-stone,’ by which some examples are known in Scotland, would well warrant such an idea, the word ‘cath’ in the Gaelic language signifying a battle. At either end of the historic ford over the river Erne, at Ballyshannon, may be seen two remarkable examples--to that on the northern side other stones would seem to lead. This is a significant fact in favour of the landmark theory. At the same time, we learn from the later writers of the life and labours of St. Patrick in Ireland, that he found the people worshipping certain idols in the form of stone pillars, some of which he caused to be overthrown, while upon one purposely left standing he inscribed the name of Jesus. There can be little doubt that the saint and his immediate followers, in their horror of all that was idolatrous, destroyed a large number of the pillar-stones which had been venerated and worshipped in pagan Ireland; but, nevertheless, a considerable number still remain. These, in some instances, would seem to have been consecrated to the Faith, and from having been idols were transformed into memorials of the triumph of Christianity. We are not without satisfactory evidence of such adaptation having been effected. Several, and apparently the oldest, lithic monuments may be observed rudely punched, not carved, with the figure of a primitive cross, accompanied by one or other of the inscriptions DNI, DNO, or DOM. Todd, in his _Life of St. Patrick_, has, we believe, conclusively shown the generally received idea of the sudden, and, it may be said, miraculous conversion of Ireland in the days of the saint, and in those of his immediate successors, to be wholly erroneous. Pagan practices and beliefs long remained, and to-day many myths, legends, and superstitions attest, as dying remnants, how deeply rooted were the ‘elder faiths.’ The Pillar-stone is the simplest form of all memorials; it is found in other countries in connection with ancient burial mounds or barrows. Such memorials to a departed hero, chief, or monarch were not confined to savage peoples, for the custom has descended through all stages of civilization, and the commemorative use of the pillar-stone is frequent in biblical history. Ancient Egypt furnishes notable examples of monoliths such as Cleopatra’s Needle; while the metropolis of Ireland, not to mention other cities, exhibits stupendous pillar monuments showing the ‘hero-worship’ of our forefathers, to the dead leaders Wellington and Nelson.