That the use of such strongholds in the lochs of Scotland and Ireland continued in historic times is abundantly attested. In the _Register of the Privy Council of Scotland_, under the date of 14th April 1608, one of the articles proposed to Angus M’Coneill, of Dunnyvaig, and Hector M’Clayne, of Dowart, for reducing them and their clans to obedience is:—“That the haill houssis of defence, strongholdis, and cranokis in the Yllis perteining to thame and their forsaidis sail be delyverit to His Majestie.” Three-legged pots of brass, and ewers of the forms in use from the thirteenth to the sixteenth century and later, have been found in several of the Scottish Crannog sites. The _Irish Annals_ contain frequent notices of the taking of Crannogs. For instance:—"A.D. 1436. The Crannog of Loch Laoghaire was taken by the sons of Brian O’Neill. On their arrival they set about constructing vessels to land on the Crannog in which the sons of Brian Oge then were; on which the latter came to the resolution of giving up the Crannog to O’Neill and made peace with him."—_Annals of the Four Masters._
There is no class of ancient remains within our country of which we have less precise knowledge than the Hill-Forts. The reason of this is not their rarity, because they form perhaps the most numerous and widely-distributed class of ancient structures now existing. But the ordinary methods of obtaining precise knowledge of their form, structure, and contents have not been applied to them, and the ordinary agencies of destruction, incident to a high condition of social and agricultural progress, have long been busy amongst them.
They differ essentially from all other constructions, because they are adaptations of naturally elevated sites for defensive purposes. The natural site is the defensive position, and the fort itself derives its form and in many cases also its character of construction from the form and nature of the eminence or promontory on which it is built. It would, therefore, be contrary to the nature of the circumstances to expect that they should exhibit any such uniformity of plan or structure as is so conspicuous in the case of the Brochs. Yet it is clear, from the little we do know of them, that there are certain groups possessing certain features of construction in common which differ from other groups possessing other features of construction in common; and it is evident that if a sufficient body of available materials existed on record regarding the different members of these groups their typical characteristics might be readily deduced. But before this can be done with that precision and certainty which are requisite for scientific work, it is necessary (1) that a series of plans and sections to scale of a sufficient number of examples from each of the various groups should be obtained; (2) that a series of observations as to the methods of construction employed in different circumstances and situations should be made; and (3) that a series of examinations of the enclosed areas and surrounding ground should be undertaken, with the view of ascertaining the character of the relics that are associated with the structures. In the meantime it is only possible to indicate some of their general characteristics as exhibited by a few of the better known examples.