3. That they were designed to answer at least a twofold purpose--to serve as belfries, and as keeps or places of strength, in which the sacred utensils, books, relics, and other valuables were deposited, and into which the ecclesiastics to whom they belonged could retire for security in cases of sudden attack. 4. An examination of ancient Irish literature tends strongly to the conclusion that the people so generally recognised this use of the round towers as a primary one, that they very rarely applied to a tower erected for defence any other term but that of ‘cloictheach’ or belfry. 5. That they were probably also used, when occasion required, as beacons and watch-towers. Petrie, while establishing their ecclesiastical character and origin, gave, however, too wide a margin to the date of their erection, viz., from the sixth century to the thirteenth. The investigations of the late Lord Dunraven in tracing such structures on the Continent narrowed their first erection down to the ninth century. He shows that they were founded on European examples, the most notable being those of Ravenna, where six of its round towers still stand. The round towers were due to Byzantine influences, and some writers trace their original source to the towers built in connection with early Syrian churches. Miss Stokes, following Lord Dunraven, assigns the Irish round towers to three periods between 890 and 1238 A.D., and classifies them into four distinct groups, according to their style of masonry and doorways. [Illustration: Doorway, Round Tower, Glendalough.] The Norse sea-rovers rendered ecclesiastical establishments most unsafe. The first period of their invasions extended from the end of the eighth century to the middle of the ninth century, and the land was ravaged from north to south with fire and sword. On the sea-coast and along the river valleys the country lay waste. On the banks of the Bann, the shores of Lough Neagh, by the Boyne, and broad expansions of the Shannon, and as far south as the distant Skellig Rock, few sacred establishments escaped plunder and desecration. To protect their churches, oratories, and sacred treasures, these towers were built by the monks, from which watch could be kept, and an easy retreat made to them as places of safety; their lines can still be traced along the shores of the waters where the fleets of the Danes are known to have appeared. The usual features of the round towers may be thus summarised: * * * * * [Illustration: Cross over the Doorway of Antrim Tower.] [Illustration: Doorway, Donaghmore Tower, Co. Meath.]