As the English settlement here became very insecure towards the close of the fourteenth century, and was peculiarly exposed to the hostile attacks of the native Irish, who continued powerful in its immediate vicinity, a grant of ten marks annually was made by King Edward III. in 1371, to the Prior of this monastery, for the repairing and rebuilding of the house, which grant was renewed six years afterwards; and in 1378, Richard II., in consideration of the great labour, burden, and expense which the Priors had in supporting their house, and the bridge contiguous to it, against the king’s enemies, granted to the Priors an annual pension of twenty marks out of the rents of the town of Newcastle of Lyons, which grant he confirmed to them in 1394, and which was ratified by his successors Henry IV. and V. in the first years of their reigns (1399, 1412), the latter monarch ordering at the same time that all arrears of rent then due should be paid.
In the civil wars of the sixteenth and seventeenth centuries the possession of Leighlin-Bridge and its castle became an object of much importance to the combatants on both sides. In 1577, when the celebrated chieftain of Leix, Rory Oge O’More, rose in rebellion, among other depredations he burned a part of the town of Leighlin-Bridge, and endeavoured to get possession of its castle, which was then feebly garrisoned under the command of Sir George Carew, constable of the fort and town. With the slender force of seven horse, as it is stated by Hooker, but under the cover of night, Carew made a sally on his assailants, numbering two hundred and forty, who, being taken by surprise, lost many men, and the remainder for a time fled. Having soon however discovered the extremely small force by which they had been attacked, they rallied, and in turn became the assailants, pursuing Carew’s party to the gate of Leighlin-Bridge Castle, and some of them even entering within its walls; but by the bravery of the garrison they were soon expelled. Carew had two men and one horse killed, and every man of his party was wounded. The rebels lost sixteen men, among whom was one of their leaders, which so discomfited them that they retired, leaving one-half of the town uninjured.