Irish Antiquarian remains may be generally classified under three heads:--I. Prehistoric, embracing those which are considered to have existed previous to, or within a limited period after, the introduction of Christianity in the fifth century; II. The Early Christian; and III. The Anglo-Irish. The Prehistoric remains consist of cromlechs, pillar-stones, cairns, stone circles, tumuli, raths, stone forts, beehive huts, rock-markings, weapons, &c. They are found in considerable numbers particularly in the more remote parts of the island, where they have been suffered to remain, many more or less unmolested, save by the hand of time. Early Christian remains are very numerous, and consist of oratories, churches, round towers, Ogam stones, and crosses. Of the early churches of Ireland--structures of a period when the ‘Scotish (Irish) monkes in Ireland and Britaine highly excelled in their holinesse and learning, _yea, sent forth whole flockes of most devout men into all parts of Europe_’[1]--there are examples in a sufficient state of preservation to give a good idea of architecture, in what may be considered its second stage in Ireland. The remains of what may be termed ‘Anglo-Irish’ structures were erected about the period of the English invasion, and although of Irish foundation, they appear generally to have been built upon Anglo-Norman or English models. The great barons who, in the time of Henry the Second, or of his immediate successors, received grants of land from the Crown, erected fortresses of considerable strength and extent, in order to preserve their possessions from the inroads of the native Irish, with whom they were usually at war. The castles of Howth, Malahide, Maynooth, Trim, Carlow, and many others, are silent witnesses to the fact that the early invaders were occasionally obliged to place some faith in the efficacy of strong walls and towers to resist the advances of their restless neighbours, who, for several centuries subsequent to the Invasion, were rather the levellers than the builders of castles. Of the massive square keep, so common in every part of the kingdom, but especially within the English Pale, the Dublin neighbourhood furnishes several examples. As, except in some minor details, they usually bear a great resemblance to each other, an inspection of one or two will afford a just idea of all. They were generally used as the residence of a chieftain, or as an outpost dependent upon some larger fortress in the neighbourhood. Many appear to have been erected by English settlers, and they are usually furnished with a bawn, or enclosure, into which cattle were driven at night, a precaution very significant of the times.