The two round towers are by far the most interesting and beautiful buildings in Clonmacnois. The larger one wants apparently twenty or thirty feet of the top; whether it was struck by lightning, or knocked off by cannon, no one seems to know. The smaller tower is as perfect as it was when its builder pronounced it finished a thousand years ago. No more beautiful piece of architecture in the way of a tower ever was erected. It seems to be absolute perfection. The most skilled modern artisan in stone could not find an imperfection in it. It is built entirely of cut stones. The roof or dome is made of lozenge-shaped stones, fitted so closely and finished so well that time and weather seem to have passed over it in vain, for it is, as far as can be seen from the ground at its base, as perfect as it ever was. Of all round towers in Ireland, it is the most beautiful and perfect. The larger tower seems to have been built of stones similar to those of the smaller one, but as it wants its top its beauty is almost entirely spoiled. What remains of it seems about as perfect in its architecture as human hands could make it. The smaller tower appears to afford positive proof of Petrie's theory as to the post-Christian origin of the Irish round towers, for it and the little church or oratory at its base, and out of which it rises, were evidently built at the same time, for the walls of both are actually in some places one. Like some few of the existing round towers (the one near Navan, for instance), the smaller one at Clonmacnois has no opening in the roof by which the sound of bells could be emitted, showing clearly that it could never have been erected solely for a belfry; for no matter how big a bell might be, its sound would not have been heard a hundred yards away, if rung under the windowless stone roof of this most perfect and beautiful of Irish round towers. That round towers were sometimes used as belfries seems very probable; but that their principal use, and the prime object for which they were erected, were to protect the clergy and the treasures of the churches from the marauding Northmen is the theory regarding them that is now most generally accepted.