Tomrair is reported to have been killed at the Battle of Sciath Nechtain, a conflict in which twelve hundred Vikings were slain, battling the combined forces of Ólchobar mac Cináeda, King of Munster and Lorcán mac Cellaig, King of Leinster, in 848.

Surviving accounts of Tomrair's demise accord him the Gaelic title erell, making him the first earl noted by Irish sources.

Afterwards in 853, a certain Amlaíb, described as the son of the King of Laithlind is stated to have won the submission of the Vikings in Ireland, and to have gained tribute from the Irish.

Tomrair's eminent standing as a Viking tánaise ríg could indicate that it was his defeat and death that is referred to by a Frankish annal in 848.

It is possible that a hoard of Carolingian coins, unearthed at Mullaghboden in the nineteenth century, may have been deposited in the context of Tomrair's defeat.

These objects appear to have formed part of the royal insignia of Dublin, and may have been symbols of the Uí Ímair dynasty descended from Ímar.

[14] These accounts reveal that Tomrair—accorded the title of earl, and described as tánaise ríg of Laithlind—fell with twelve hundred Vikings at the Battle of Sciath Nechtain,[15] a conflict evidently fought at Skenagun in the parish of Castledermot.

[21] According to various annalistic accounts, the said king sent a fleet of one hundred and forty ships overseas to contend with Vikings already settled in Ireland.

[22][note 3] In 851, a contingent of Dubgaill are stated to have arrived in Dublin, where they defeated the Finngaill before overcoming them again at Linn Duachaill.

[27][note 5] Although the annal-entries that report this event are the first specific notices of Amlaíb by name, he may well have commanded the Vikings of Laithlind in the earlier attested conflicts.

[33] The eleventh-century Fragmentary Annals of Ireland certainly claims that the three were brothers,[34][note 6] and specifically identifies the father of Amlaíb and Ímar as a man named Gofraid.

[52][note 8] The earliest instance of the Gaelic title erell (later ı́arla) is the account of Tomrair's demise reported by the Annals of Ulster.

[60] The Scandinavian title of jarl referred to a king's subordinate or deputy, a man who held some form of vice-regal authority over a particular region.

[89] If correct, Tomrair's demise in 848 may well have been seized upon by the Dubgaill early in the 850s, which in turn precipitated a retaliatory response from the King of Laithlind in the form of an 853 invasion to restore hegemony in Ireland.

If correct, Amlaíb's dramatic arrival in Ireland, following the temporary intrusion by the Dubgaill, would seem to have resulted in a period of reconciliation between both parties.

The subsequent actions of the Vikings of Laithlind may have been undertaken in the specific context of recovering control of an important node in their trade network.

[100] Such conflict between competing Danish and Norwegian interests in the Irish Sea region could also represent an early phase in the eventual consolidation of royal power in Norway.

[103] There is reason to suspect that this dynasty reinforced its right to rule by way of royal insignia specifically recorded by the Irish annals.

[110] The various accounts of the sword and ring reveal that the objects were powerful ceremonial symbols, and important parts of Dublin's royal regalia.

[120] It is possible that the eponym of the ring is identical to that of Caill Tomair ("The Wood of Tomar"),[121] a forest seemingly situated north of Dublin,[122] attested in the late tenth century by the Annals of Inisfallen,[123] the Annals of Tigernach,[124] the twelfth-century Cogad Gáedel re Gallaib,[125] and Chronicon Scotorum.

[126] The wood has been specifically associated with Þór,[127] and regarded to have been a place of pagan significance in Viking Age Ireland.

[128] If the ring was indeed a reference to a heathen cult object, the fact that only the sword is attested in the tenth century could indicate that an association between the dynasty and a pagan item was undesirable.

[130][note 13] Although Irish sources reveal that at least three later Vikings bore the same name,[136] Tomrair was clearly the most eminent of these individuals.

[154] Although any of the Irish victories of 848 could have inspired a Frankish chronicler to make note of the island,[155] it could well have been Tomrair's eminent status—and his ultimate destruction—that was the true catalyst for this overseas annal-entry.

[159] The hoard itself appears to have been composed of coins looted from Aquitaine only a few years previous,[160] a haul possibly pillaged by the Viking fleet of Westfaldingi contemporaneously attested by the ninth–eleventh-century Annales Engolismenses.