The Sack of Cashel (also known as the Massacre of Cashel) is a notorious atrocity which occurs in County Tipperary on September 15, 1647, during the Irish Confederate Wars, part of the Wars of the Three Kingdoms.

In the summer of 1647, Murrough O’Brien, 6th Baron Inchiquin, the Irish Protestant commander of the Protestant army of Cork, commences a campaign against the Irish Catholic strongholds in Munster. The counties of Limerick and Clare are raided, and he soon turns his attention to the bountiful eastern counties of Munster. In early September, his forces quickly take the Cahir Castle in Tipperary. This strong castle is well positioned to become a base for the Cork Protestant army, and it is used to raid and devastate the surrounding countryside. The Munster army under Lord Taaffe does not make any serious effort to oppose Inchiquin, probably the result of the political scheming of Donough MacCarty, 2nd Viscount Muskerry and other powerful Irish lords who hope to keep the Munster army intact for their own ends. As such, Inchiquin is allowed to make a major push towards the town and ecclesiastical centre of Cashel.

Inchiquin has already launched two minor raids against Cashel, and he now has the opportunity to launch a major assault. The Parliamentarian forces first storm nearby Roche Castle, putting fifty warders to the sword. This attack terrifies the local inhabitants of the region, some of whom flee to hiding places, while hundreds of others flee promptly to the Rock of Cashel, a stronger place than the town itself. Lord Taaffe has placed six companies in the fortified churchyard that sits upon the rock, and considers the place defensible, though he himself does not stay to put it to the test, leaving command to the Governor Lieutenant-Colonel Butler.

Arriving with his army at the Rock, Inchiquin calls for surrender within an hour. The defenders of the churchyard offer to negotiate but that is refused, and on the afternoon of September 15 the assault commences. The Parliamentarians are first reminded of earlier atrocities against Protestants, and then begin to deploy. The attack is led by around 150 dismounted horse officers with the remainder of the infantry following. Troops of horse ride along the flanks of the advancing force to encourage the infantry. The Irish soldiers attempt to drive off the attackers with pikes while the civilians inside hurl rocks down from the walls. In turn the attackers hurl firebrands into the compound, setting some of the buildings inside on fire. Although many are wounded, the Parliamentarians gradually fight their way over the walls, pushing the garrison into the church.

Initially, the Irish defenders manage to protect the Church, holding off the attackers trying to get through the doors, but the Parliamentarians then place numerous ladders against the many windows in the church and swarm the building. For another half an hour fighting rages inside the church, until the depleted defenders retreat up the bell tower. Only sixty soldiers of the garrison remain at this point, and they thus accept a call to surrender. However, after they have descended the tower and thrown their swords away, all are killed.

In the end all the soldiers and most of the civilians on the Rock are killed by the attackers. The Bishop and Mayor of Cashel along with a few others survive by taking shelter in a secret hiding place. Apart from these a few women are spared, after being stripped of their clothes, and a small number of wealthy civilians are taken prisoner, but these are the exceptions. Overall, close to 1,000 are killed, amongst them Lieutenant-Colonel Butler and catholic scholar Theobald Stapleton. The bodies in the churchyard are described by a witness as being five or six deep.

The slaughter is followed by extensive looting. There is much of value inside, for apart from pictures, chalices and vestments of the church, many of the slain civilians had also brought their valuables with them. The sword and ceremonial mace of the mayor of Cashel, as well as the coach of the bishop are captured. The plunder is accompanied by acts of iconoclasm, with statues smashed and pictures defaced. The deserted town of Cashel is also torched.

The atrocity at Cashel causes a deep impact in Ireland, as it is the worst single atrocity committed in Ireland since the start of fighting in 1641. Previously, the most infamous massacre amongst the Catholic population is that at Timolin in 1643, when 200 civilians are killed by James Butler, 1st Duke of Ormond‘s English Royalist army, but many more than this are killed at Cashel, and the Rock of Cashel is one of the chief holy places of Ireland. The slaughter of the garrison at Cashel and the subsequent devastation of Catholic held Munster earns Inchiquin the Irish nickname, Murchadh na Dóiteáin or “Murrough of the Burnings.”