Wexford Bridge Massacre
In the great Irish Rebellion of 1798, May 25th, some 14,000 Irish insurgents attacked Wexford, defeated the garrison, put to death all those taken prisoners, and on the 30th frightened the town into a surrender. They treated the Protestants with the utmost barbarity, and, after taking Enniscorthy, encamped on Vinegar Hill (q.v.). When informed that Wexford was retaken by the English, the insurgents massacred about a thousand Protestant prisoners in cold blood.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894