Boru the Administrator and the Heathen Danes: O'Halloran's Vision of Irish History

Sylvester O'Halloran (1728–1807) was a Clare-born surgeon and historian who sought to defend Ireland and its past from detractors. He wrote a number of historical works:

  • An introduction to the study of the antiquities of Ireland (1770)
  • Ierne defended (1774)
  • A general history of Ireland (1775)

Critics were divided on the value and accuracy of these histories, which were written in an emotional and flowery style, as the passages below demonstrate.

Brian Boru and the Vikings in A General History of Ireland

In his General History of Ireland, O'Halloran presented the Vikings as cruel and warlike attackers; and in this particular passage, the natural world mirrored the depredations of the Vikings:

[The Viking] troops suddenly landed, at different times, on both sides of the Shannon, and Corcabaiscan, and Tradeuighe on the north, and Ui Connal Gabhra on the south side, with all the churches, were laid in ashes [burned]. A large party of these incendiaries were, however, overtaken at Seannued near Glin, and put to the sword.

But though it appears, that whenever the Irish and these foreigners met, the latter were, in general, defeated, yet the country was destroyed beforehand by reason of their commanding the sea, and being at all times able to land where least expected.

Though the ravages of these Danes were alone as much afflictions as could be well borne, yet the very elements seemed to conspire to the ruin of this afflicted kingdom.

On the northern side of the Shannon, in the month of March following, such violent and uncommon claps of thunder and lightning burst forth, that above a thousand people were destroyed by it; at the same time the sea broke down the banks with great violence, and laid a considerable part of the country under water."

Brian Boru: Diplomatic, Pious, and Efficient.

In contrast to his depiction of the Vikings, O’Halloran presented a positive picture of the Irish king.  He described Boru and the political situation in Ireland in terms much more appropriate to the eighteenth century than the eleventh, and in contrast to the 'heathen Danes'.

Having wisely regulated the national system, Brian dissolved the assembly, and sent ambassadors … to the different princes of Europe, announcing his election to the Irish monarchy.  With these embassies were sent presents of fine horse, wolf-dogs, and hawks &c.

His next care was to see the laws every where executed with strictness and impartiality, and the money appropriated to public uses, justly applied.  It was astonishing to see what a new face the whole kingdom assumed, in a short time, through his care and attention.  The cities, from a ruined state, became more ample and splendid; the churches, monasteries, and public hospitals were repaired or rebuilt with additional majesty; and piety, peace, and plenty spread far and wide!

The edict, which he published when king of Munster, against the heathen Danes, had so visible an effect on the conduct and morals of that barbarous people, that it became now national; and this, with the exhortations and examples of the clergy, wonderfully facilitated the conversion and civilization of them."

O'Halloran's Life and Education

As a young man he studied surgery in London, Paris and Leyden before returning to Ireland and establishing a surgery in Limerick in 1749 and marrying a Limerick woman, Mary Casey.

His time spent abroad gave him a particular Parisian style:

He created a stir, his tall slender figure attired in French costume, and with an impressive wig, cocked hat, and gold-headed cane."

J. B. Lyons, ‘O'Halloran, Sylvester’ in Dictionary of Irish Biography.


O’Halloran’s interests were varied, and he published a number of well-received treaties.

One of his particular interests was in investigating the causes of cataracts.  As part of his investigations he examined the eyes of dead calves and even conducted experiments on live dogs. 

O’Halloran also turned his attention to the properties of air, amputation, head injuries and surgery in general – writing and publishing on some of these topics.


© The National Gallery, London 2014

Did you know?  O'Halloran was passionate about defending Ireland and the Irish from those who might denigrate it, and this was evident even in his medical works. In 'A New Treatise on External Injuries of the Head (1793)' he wrote about the Irish temper, and how it had been exacerbated by the 'cruel oppressions' of the British administration: 

our people, invincibly brave, notwithstanding the cruel oppressions they have suffered for a century past, and highly irritable, soon catch fire: a slight offence is frequently followed by serious consequences; and sticks, stones, and every other species of offence next to hand, are dealt out with great liberality!"

O’Halloran was also involved in the eighteenth-century Limerick intellectual society and as a man of letters, he corresponded with many intellectuals of his day, including Edmund Burke. 

Did you know?  O'Halloran conveyed bladders full of air around Limerick, climbing up the tallest buildings and hills to see if altitude changed the properties of air. His conclusion? Nope!



John Gilborne, The Medical Review, 1775; [W. R. Wilde], ‘Illustrious physicians and surgeons in Ireland. No. VI. Sylvester O'Halloran, M.R.I.A.’, Dublin Quart. Jn. Med. Sc., v (1848), pp 223–50

Kevin Hannan, ‘A forgotten Limerick genius’, Old Limerick Jn., xxii (1987), pp 4–7.

Claire E. Lyons, ‘Sylvester O’Halloran (1727-1807)¸ Three unpublished letters’ in North Munster Antiquarian Journal, no. 49 (2009).

J. B. Lyons, 'O'Halloran, Sylvester' Dictionary of Irish Biography, (eds) James McGuire and James Quinn (Cambridge University Press, 2009)

J. B. Lyons, ‘Sylvester O'Halloran’, Ir. Jn. Med. Sc. (1963), pp 217–32, 279–88.

J. B. Lyons, ‘The letters of Sylvester O'Halloran’, N. Munster Antiq. Jn., ix (1963), pp 163–81.

J. B. Lyons, ‘Sylvester O' Halloran's treatise on the air’, Ire. Med. Jn., lxxvi (1983), pp 37–9.

Clare. O’Halloran, ‘Sylvester O’Halloran (1727-1807)’ in The Oxford Dictionary of National Biography Online.

Clare O'Halloran, "Brian Boru and his afterlife", in History of Ireland, vol. 22, no. 2 (2014) pp 38-41.

Clare O'Halloran, ‘The Island of Saints and Scholars’: Views of the early church and sectarian politics in late-eighteenth century Ireland’ in Eighteenth-Century Ireland, vol. 5 (1990), pp 7-20.               

Clare O'Halloran, ‘The Triumph of ‘Virtuous Liberty’: Representations of the Vikings and Brian Boru in eighteenth-century histories’ in Eighteenth-Century Ireland, vol. 22 (2007), pp 151-163.

As an ophthalmological experiment, O'Halloran hung dogs upside down to see if increased blood flow to the eyes caused cataracts.