The Defenders were a Roman Catholic agrarian secret society in 18th-century Ireland, founded in County Armagh. Initially, they were formed as local defensive organisations opposed to the Protestant Peep o' Day Boys; however, by 1790 had become a secret oath-bound fraternal society made up of lodges. By 1796, the Defenders had allied with the United Irishmen, and participated in the 1798 rebellion. By the 19th century, the organisation had developed into the Ribbonmen.
The Defenders were formed in the mid-1780s by Catholics in response to the failure of the authorities to take action against the Protestant Peep o' Day Boys who launched nighttime raids on Catholic homes under the pretence of confiscating arms which Catholics were prohibited from possessing under the terms of the Penal Laws.
Having seen the fighting between the Nappach Fleet, Bunker's Hill Defenders, and the Bawn Fleet, between 1784 and 1785 go largely unpunished, they were encouraged to form their own grouping. At Grangemore, near Ballymacnab, County Armagh, an area that had previously suffered from a Peep o' Day Boys raid, such a grouping was founded and became known as the Defenders. Supplied with arms purchased from a Protestant shopkeeper in Armagh, they embarked on night-watches and patrols keeping an eye out for Peep o' Day Boys.
The Defenders started out as independent local groups, defensive in nature, however by 1790 they had merged into a widespread secret oath-bound fraternal organisation consisting of lodges, associated to a head-lodge led by a Grand Master and committee. The Defenders were greatly influenced by Freemasonry, and were made up of the lower class of Catholics. Each member had to swear an oath, which despite the penal laws which they were subject to, included the swearing of obedience to King George the Third, his successors, and the government. The oath itself was revised several times, but kept its central character whilst focusing more on loyalty and solidarity.