Massacre of Mullaghmast

The Massacre of Mullaghmast (Irish: Ár Mhullach Maistean) refers to a summary execution of Irish gentry by the English Army in Ireland. It probably occurred at the end of the year 1577. There is limited surviving documentation on the massacre, although documents have recently been made available at the National Library of Ireland.

Francis Cosby, a soldier, and Robert Hartpole, a colonist, were both Englishmen who were granted land in the plantation of Leix (formally known as the Queen's county) in Ireland. The men befriended the native Irish, but in conjunction with the Lord deputy in Ireland plotted to kill the local Chieftains, two of whom were high-powered Ulstermen. With the help of the Lord Deputy of Ireland, they summoned 100-400 of the members of the leading families of Laois to Mullaghmast in County Kildare to perform military service. Most of these people were slaughtered, some burned at the stake.

An account of the massacre:

In the year 1705, there was an old gentleman of the name of Cullen, in the County Kildare, who often discoursed with one Dwyer and one Dowling, actually living at Mullaghmast when this horrid murder was committed, which was about the sixteenth year (recté, nineteenth) of Queen Elizabeth's reign; and the account he gives of it is, that those who were chiefly concerned in this horrid murder were the Deavils, the Grehams, the Cosbys, the Piggotts, the Bowens, the Hartpoles, the Hovendons, the Dempsys, and the FitzGeralds. The last five of these were, at that time, Roman Catholics, by whom the poor people murdered at Mullaghmast were chiefly invited there, in pretence that said people should enter into an alliance offensive and defensive with them. But their reception was to put them all to death, except one O'More, who was the only person that escaped. Notwithstanding what is said that one O'More only had escaped the massacre, yet the common tradition of the country is, that many more had escaped through the means of one Henry Lalor, who, remarking that none of those returned who had entered the fort before him, desired his companions to make off as fast as they could, in case they did not see him come back. Said Lalor, as he was entering the fort, saw the carcasses of his slaughtered companions ; then drew his sword, and fought his way back to those that survived, along with whom he made his escape to Dysart, his family's ancestral home.

...
Wikipedia