When we speak of the "Danes" in Irish history we really mean the Vikings, and they were mostly Norwegians. The term "Vikings" was applied, in the first instance, to bands of sea-rovers, bent on plunder, who in their excellent boats began to harass the coastlands of Western Europe and its islands near the end of the eighth century.
The first Viking raid was directed against the island monastery of Lindisfarne, off the coast of Northumbria in England, in A.D. 793. The more famous monastery of Iona was looted in 795; and in the same year, Ireland had its first visitation from these marauders, The island of Rechru, near Dublin, was plundered. This was also a monastic site; and today it bears, significantly, the Viking name of Lamb-ey (Lambay). These first hit-and-run raiders were Norwegians; it was not till A.D. 849 that the Danes began to take a hand in the game in Ireland.
The Vikings were interested in all kinds of loot, including able young men and women, for whom they found a ready sale in the slave-markets of northern Europe. But their main interest was in silver. It was this that attracted them to monasteries and churches. Here they were sure to find silver vessels, like chalices, and sometimes precious ornaments on decorated shrines. Being still pagans, they regarded Christian buildings as so many treasure-houses, fit only to be plundered and often burned. One of the most serious consequences of these depredations was the disruption of the great monastic schools, like those of Armagh, Bangor and Clonmacnois. But, more serious still, was the wholesale destruction of monastic records and other manuscripts. This was an irreparable loss from which we suffer still.
Encouraged by their initial successes, the Vikings kept on coming in ever larger fleets. Nor were they long content to hit and run. Before the middle of the ninth century they had effected settlements on the main harbours of the country and had laid the foundations of such cities as Dublin, Waterford, Cork, and Limerick. At the same time, they began to sail up the navigable rivers into the inland lakes such as Lough Ree on the Shannon, Lough Erne and Lough Neagh; and from these bases they ravaged the interior of the country.
From their maritime settlements they entered into international trade and played an important, if troublesome, part in the political life of Ireland. By his victory at Clontarf in A.D. 1014, the great high-king Brian Boru, effectively checked the political ambitions of the Vikings in Ireland. But he did not destroy their settlements. These remained. And gradually the settlers accepted Christianity and were absorbed into the population of the country. Our best source of information on the Vikings in Ireland is "The Annals of Ulster". From this source we first hear of the Vikings on Lough Neagh in the year 839 A.D. when, we are told, they despoiled the territories and churches of the north of Ireland, from Lough Neagh. From other sources we learn that a powerful Norwegian leader, named Turgesius, was active in the north from A.D. 831 till 845, and that he had a fleet on Lough Neagh among other places.
In 840, we are told the Vikings pillaged Louth from Lough Neagh, led some bishops, priests and sages captive and slew others. The following year they were still on the Lough; but their activities are not recorded.
After this we have no record of Viking activity on Lough Neagh for nearly a century. In A.D. 928, however, a fleet of Vikings, led by the son of Ailche, plundered the islands of Lough Neagh and its borders. This son of Ailche, whose real name was Gormo Gamle, was a very active depredator. We hear of him operating also from the Viking settlement of Limerick. On one occasion he sailed up the Shannon to Lough Ree and from there he destroyed Clonmacnois and all the islands of the lake "and carried off a great spoil between gold and silver and other treasures."
Under the year 930, we are told that the "foreigners" (Vikings) were on Lough Neagh and their encampment was at Rubha Menna. This place has been identified as the spot where the River Maine enters the Lough, near Shane's Castle in County Antrim;
Finally, the "Annals of Ulster" tell us that in the year 945, the "foreigners" of Lough Neagh were killed and their fleet destroyed by Donnall and his brother, sons of Murtagh. This Donnall and his brother were O'Neills; and among the very first to bear this famous name. They were, in fact, grandsons of the high-king, Niall Glundubh; and it is from him that all true members of the O'Neill clan take their name; for the name, O'Neill, means literally "Grandson of Niall" (Glundubh). Niall himself was killed in battle against the Vikings of Dublin in A.D. 919.
It is pretty certain that the "Annals" do not give us the full tale of the Vikings fleets that infested Lough Neagh; but they give us evidence enough that all the lands within striking distance of Lough Neagh's banks suffered again and again from the foul attentions of these marauders, with their attendant plundering and arson and slaughter. We can be sure that the churches and monasteries of these areas came in for more than their share of these attentions.
In what we may now call the Craigavon area, we know of two monasteries that were in existence before the Viking period. One of these was St. Gobhan's, from which Seagoe takes its name. The other was St. Evin's which gave its name to the townland of Taghnevan in Lurgan. We do not know whether either of them survived the Viking raids. There is no reference to Seagoe in any surviving document for over three hundred years after the Viking period and, by then, the ancient site was occupied by a parish church. The monastery of Taghnevan is not mentioned in any known document of any period. We know of its existence only from the name, plus the fact that the ordnance surveyors noted about 1834 that there was a plot of ground in this townland that had never been ploughed. This spot, held sacred by generations of land-hungry farmers, probably marked the site of the monastery, or rather, perhaps, of the graveyard attached to it. The evidence, such as it is, suggests that the site was abandoned at a relatively early date.
At least one relic of the Viking presence on Lough Neagh survives to this day. It is the name, "Oxford Island", now well known as the site of the Marina created by the Craigavon Commission. Here the word, Oxford, represents the pure Norse, Ost-Fjord, East inlet.