Seven years after the Anglo-Norman invasion the county was attacked by Miles de Cogan, one of the English adventurers, who was l joined by Murrough, son of Roderic, king of Ireland, at the head of a body of malcontents. The natives, by driving away their cattle and laying waste the country, exposed De Cogan and his army to great danger from famine, and compelled them to retreat. In 1204 the county was ravaged by William do Burge Fitz-Aldelm, lord of Limerick ; in 1216 the castle of Athlone was erected to command the ford of the Shannon ; and in 1268 that of Roscommon was built to secure the-quietness of the county. In 1315 Richard de Burgo, earl of Ulster, and Phelim O'Conor, prince of Connaught, advanced from Roscommon to repel the invasion of the Scotch under Edward Brucc ; but O'Conor entered into • secret treaty with Bruce, and retired to defend his own territory against the usurpation of his kinsman Roderic, whom with the aid of the English he defeated and Blew. Having then avowed his alliance with the Scotch, be was attacked and completely defeated at Athenry in Galway by the English under William de Burge, the earl's brother, and Sir John Bellingham. This victory broke the power of the O'Coners. Meanwhile the inheritance of the De Burgos was conveyed by marriage to Lionel, duke of Clarence, son of Edward III., whose descendants came to the throne in the person of Edward 1V. In the reign of Elizabeth, Connaught was divided into counties, and the county of Roscommon into baronies. The O'Conors remained loyal during the troubles of Elizabeth's reign, but in the rebellion of 1641 the O'Conor Don took part with the Ulster insurgents after they had made themselves masters of the county. At the close
of the war his estates, with those of other chiefs, were confiscated and divided among English and Scotch adventurers. At the restoration however he recovered the greater part of his property, and his descendants are among the few native Irish families who retain their lands.
The most numerous antiquities of the county are the raths, or hill forts, of which nearly 500 have been reckoned. They are found upon natural eminences, and are formed generally of earth and hurdles, but sometimes of wooden walls, resting on a foundation of earth, and inclose the dwelling-place of the chieftain and his family. They are regarded with reverence, and left in most cases undisturbed by the plough. At Oran, between Roscommon and Castlerea, there is a portion of a round tower 12 feet high, built of limestone in regular courses, with finely-cut and close-fitting stones. Near Lough Glynn are the ruins of a fort of unknown antiquity. The massive walls and polygonal towers of Ballintobber Castle, the ancient stronghold of the O'Conor Don, are in tolerable preservation. Other feudal remains are, those of Roscommon Castle, the keep of Athlone Castle, the ruins of a small castle on Castle Island in Lough Key, and those of Coots Hall, a fortified mansion of the middle ages, between Lough Key and the Shannon. The principal ecclesiastical antiquities are the ruins of Boyle, Roscommon, Ts:tisk, and Clonshanville abbeys. There are numerous remains of old churches, inclosed within cemeteries still in use.