To begin with it should be noted that there is not as such a thing legally as "clan arms". Historically, all heraldic arms are the personal property of an armiger, by grant or inheritance by confirmation.
The arms of the armigerous O’Donnells of Tyrconnell derive from those legendarily bestowed in the 5th century on Conall, progenitor of the Cenel Conaill people and after whom the land of Tír Chonaill is called, and of which the O’Donnells were the kings and princes for many centuries.
Whilst coats-of-arms were not generally assumed as heraldic devices until the 12th century, shields and banners have been emblazoned with symbols of their bearers from the most ancient antiquity, as evidenced from Roman times and the Labarum of Constantine.
The antiquity of the use of an individualized identifying shield by Irish nobles pre-dates the emergence of “coats of arms” (originally worn over suits of armour) in feudal Europe, as evidenced by the historical record in Foras Feasa ar Éirinn - History of Ireland, Part II, Book I, Chapter XXXIX, written by Geoffrey Keating, D.D., completed in 1633/1634 (and translated and edited by Rev. Patrick S. Dineen and published by the Irish Texts Society, London, 1908) wherein the author describes the times and legacy of King Tuathal Teachtmhar (about two thousand years ago) and how the nobles attending the triennial Feis at Tara, the ancient royal capital of Ireland, were seated below their individual shields, marks of their identity, which hung by hook from a beam which ran the length of the banqueting hall, so placed by the bollsaire (marshall of the house) on the instructions of the seancha, having taken it from the shield-bearer of the noble concerned, ranked according to his title.
According to further ancient sources, such as the Life and Acts of Saint Patrick (chapter 138) by Jocelyn of Furness (c. 1185 AD; he was so commissioned by Sir John de Courcy, according to John O’Donovan in his translation of the Annals of the Four Masters, vol. III, p.33), St. Patrick took his staff, known as the staff of Jesus, or Bacall Iosa, and struck the shield of Prince Conall, son of the High King of Ireland, Niall Naoigeallaigh, rendering a sign of the Cross on it,
et mox cum baculo suo, qui baculus Jesu dicebatur Crucis signum ejus scuto impressit, asserens neminem de stirpe ejus in bello vincendum qui signum illud,
and told him that those who would bear that sign in battle would be victorious, and that many saints and nations would proceed from him and be blessed.
This clearly was intended as a spiritual vocation, a religious duty, more than as a device of military valour. Furthermore, from the perspective of later heraldic significance, and on a vexillogical level as such, the bestowal of the symbol of the Holy Cross on the shield of a prince of the royal family of Ireland, a fons honoris in its own regal right, by the Church’s Apostle of Ireland, St. Patrick, can be seen as a very early exercise of the Holy See’s supreme authority as the ultimate fons honoris, being the overlord of all royalty in those times, the era of Christendom, and through whom the “divine right” of kings to rule was consecrated (vide so-called “Donation of Constantine”).
This origin of these arms was also recorded by the medieval Gaelic poet Eoin Ruadh Mac an Bhaird who composed a poem recounting the ancient tradition that these arms were granted by St. Patrick, written in the Lebhar Inghine I Dhomhnaill – the Book of O’Donnell’s Daughter, written in the Irish Franciscan College of Saint Anthony in Louvain in the early 1600s and held today in the Bibliothèque Royal in Brussels.
The motto ascribed has always been In Hoc Signo Vinces, recalling the vision of Emperor Constantine the Great, and his conversion at Saxa Rubra before the battle of the Milvian Bridge, and as emblazoned on the Labarum.
may well be, as speculated by some, that it was under the influence of the
infamous Inion Dubh (second wife of Sir Hugh Dubh MacManus O’Donnell, 23rd
O’Donnell) being a MacDonnell, that the O’Donnell arms took the very particular
form of a passion cross upheld by an arm – The MacDonnells/MacDonalds of
Scotland have just such a blazon emanating from a cloud. But we should not
doubt that the principal motif of the O’Donnell arms is and has always been the
Cross, and the hand clasping and arm upholding it were only ancillary features,
of probable later introduction, and not an original essential feature.
Holy Cross Abbey
Thurles, County Tipperary
by William Henry Bartlett (1809-1854)
In 1601, Hugh O’Neill and Red Hugh O’Donnell fought their way southward to link up with the Spanish and engage the English at the Battle of Kinsale. On Red Hugh’s way there, he visited Holy Cross Abbey on the Feast of Saint Andrew the First-Called Apostle, 30 November, with Donal Oge, and they venerated the a relic of the True Cross, called the Holy Rood. The relic had been discovered by Saint Helena, mother of Emperor Constantine the Great, from whom, through the conversion of Conall by Saint Patrick, the emblem of the Cross and the motto In Hoc Signo Vinces, descend as the fundamental Arms of the O’Donnells of Tyrconnell. It was after that that Red Hugh deployed Donal Oge to Ardfert.
A fragment of the relic was brought there in 1233 by Isabella of Angoulême, widow of King John. With time, Holy Cross Abbey became a place of medieval pilgrimage and a rallying-point for the dispossessed Catholics and victims of religious persecution.
During the later Flight of the Earls, Hugh O’Neill, Earl of Tyrone, and Red Hugh’s brother, Rory O’Donnell, Earl of Tyrconnell, brough a portion of the True Cross on their Flight from Ireland in 1607, which they placed in the sea, trailing behind as a token of providence.
The Holy Rood relic was last exposed for public veneration in 1632, and following the Cromwellian war, Holy Cross Abbey fell into ruins. It became a scheduled national monument in 1880, “to be preserved and not used as a place of worship”. However, as a result of a special legislation in the Dail on its 50th anniversary, 21 January 1969, the premier item passed, enabling Holy Cross Abbey to be restored as a place of Catholic worship, exceptionally for a national monument. At that time, the Vatican returned an authenticated relic of the Holy Cross, and the emblem of the Jerusalem Cross was been restored for the Abbey.