BOYNE, a river in Ireland, rising in the Bog of Allen, near Carbery in Co. Kildare and flowing in a north-easterly direction past Trim and Navan to enter the Irish sea, 4m. below Drogheda. On July I, 1690, there took place on its banks a battle between the armies of King William III. and King James II. In June William assembled south-west of Belfast an army of 35,00o men of very heterogeneous composition, including English, Northern Irish, Dutch, French Huguenot and Danish units. As soon as his advance commenced, James, who was with some 25,00o Irish and French troops at Dundalk, fell back southwards, without fighting, behind the line of the Boyne and there stood for battle. William attacked early on July I; for a time the Irish made a stout resis tance, but were finally broken when William, who had personally led his left wing across the river by fords above Drogheda, launched his cavalry against their right and rear. The Jacobite defeat was complete; James abandoned his army and fled to France, thus sealing the fate of his cause not only in Ireland but in England as well, and leaving William to occupy Dublin and complete the reconquest of the country at his leisure. The losses at the Boyne were small and the battle was in itself of little tactical importance, but its strategical consequences were decisive of the war in Ireland and of the destiny of that country for the next hundred years, and through them Protestantism as the official religion of Great Britain was made secure. The battle is com memorated by an obelisk 2 m. west of Drogheda, and is annually celebrated by Orangemen on July 12 ; the "new style" date, repre senting the "old style" July i is July 11, but July 12 was chosen, as this is the O.S. date of the battle of Aughrim (1691), and the two are celebrated together. (See GRAND ALLIANCE, WAR OF THE.)