Soon after this, in 856 and 857, the Gall-Ghaedhil or Norse-Irish, make their appearance in various parts of the island—in Meath and Ulster and Munster. These were the people of the generation following the Norse occupation of the Scottish islands and the Isle of Man. They spoke a broken Irish and no doubt also a broken Norse dialect.

In 851, a new variety of Norsemen arrives on the Irish coast. They are called the Black Heathens, the Black Foreigners, the Black Lochlannachs, in contradistinction to the Fair Heathens, Fair Foreigners, or Fair Lochlannachs who had been here before them. The Welsh chronicle, the Annales Cambriae, makes it fairly clear that these Black Heathens were the Danes. They came in hostility to the Norwegians, with whom they fought fierce battles; and we have already seen that for a number of years the Danes held the chief power in the Hebrides.

At this point of time, about the middle of the ninth century, the Norsemen must have seemed to be about to become masters of all northern Europe from the west of Ireland to the banks of the Volga. England was crumbling under their attacks. The Anglo-Saxon Chronicle tells how Norse armies marched up and down through the country without resistance, then moved off to the Continent. They occupied Ghent in Flanders for a year. They defeated the Franks in battle and supplied themselves with horses from their captures, pushed up the Meuse into France, encamped there for another year; went up the Scheldt to Condé and sat there for a year; up the Somme to Amiens, and sat there for a year. Then up the Seine, and took up their winter quarters beside Paris. Then the "army went up through the bridge at Paris, and thence up along the Seine as far as the Marne, and thence up the Marne to Cheny, and then sat down, there and on the Yonne, two winters in the two places." Then they crossed from the Seine to the borders of Brittany, where the Bretons attacked and defeated them, driving them into their ships, which apparently had been sent round by sea to co-operate with them. Turning again eastward they were defeated next year in Germany, but held together in France for two years more, when they came down to Boulogne, and finding shipping for their whole force, including horses, crossed over to England in two hundred and fifty ships, Alfred being then king in England. Afterwards they crossed England, passing up the Thames and then up the Severn. Alfred, assisted by the Welsh, defeated them. They fell back on Essex, mustered fresh forces there, once more crossed England and laid siege to Chester, invaded Wales and were driven out of it. Some settled down in the conquered lands of East Anglia and Northumbria, the rest made a fresh expedition into France. Though Alfred was a great and admirable king, and justly held up to renown in English history, he could do no more than hold a minor part of England against these invaders, and at his death in 901 they were undisputed masters of about two thirds of that country.

Several causes operated in checking the growth of Norse power. One was the rivalry between the Danes and the Norwegians. Another was the consolidation of Scotland under Cinaeth Mac Ailpin. A third cause undoubtedly was the tenacious resistance of the "Celts." Had the Norsemen been as successful in Scotland and Ireland, Wales and Brittany, as they were in England and Normandy, Harald the Fair might have been the head of a new empire. The annals give a long list of pitched battles in Ireland, in some of which the invaders were victorious but for the most part they were defeated. Mr. Orpen ascribes their failure to the fact that the Irish were not politically centralised and were therefore harder to break down; yet he goes on to censure this defect in the Irish polity. Are we to conclude that it was a misfortune for Ireland and other countries that Ireland was not subjugated by the Scandinavian Heathens?

As a matter of fact, it was under the personal command of the high-king, Aedh Finnliath, that the Irish resistance took a definitely successful turn. In 866, this king captured all the strongholds of the Norsemen in the northern half of Ireland; and from this time on, they made no settlements to the north of Dublin and Limerick. Olaf and Ivar, the two kings of Dublin, turned their arms against Britain. In 870, as already related, after a siege of four months, they captured the last stronghold of the northern Britons at Dumbarton. In recording the death of Ivar in 873, the Irish annals entitled him "king of the Norsemen of Ireland and Britain."

Ireland, however, was not at peace from the invaders. Under the same year, 873, we find a characteristic entry in the annals. I have already said that those who resort to these chronicles for a record of the normal affairs of Ireland mistake the character of the record and expose themselves to deception. One of the institutions connected with the Irish monarchy was the "Fair" or Assembly of Taillte near Navan. This was considered to be the principal assembly in Ireland, and to preside over it was a function of the king of Ireland. Yet during more than four centuries before this year 873, the Assembly is only five times mentioned, and in each instance it is not the normal fact but an abnormal incident that is recorded. In the year 717, the Assembly was disturbed by Foghartach, king of Bregia. Foghartach was a claimant to the high-kingship. In 714, he was deposed and exiled to Britain. In 716, he is recorded as reigning again. His disturbance of the Assembly of Taillte in the following year marks therefore an attempt on his part to assert his position as monarch. The effective high-king at the time was Fergal, king of Ailech. In 733, Cathal, king of Munster, made a similar attempt to preside, and was prevented by the king of Meath. After this event, there is no mention of the Assembly until 811. In that year, the Ui Néill having done something in violation of the sanctuary rights of the monastery of Tallaght near Dublin, the monastic authorities placed the Assembly under an interdict. The high-king nevertheless proceeded to hold it. He was Aedh Oirdnidhe, king of Ailech; and so we see that whether the monarch had his domestic realm in Meath or in the far North, it was equally his custom to preside over this Assembly. He failed to hold the Assembly. In face of the ban "neither horse nor chariot came thither." And the violated sanctuary of Tallaght received reparation after this in the form of many gifts.

In 827, the Assembly was broken up "against the Gailings" by the high-king Conchobor. The explanation of this event is possibly that the high-king failed to hold the Assembly, being preoccupied with the hostile activities of the Norsemen who in that year were plundering, burning and wasting the Bregian seaboard, not far from Taillte; also with the equally troublesome activities of Feidlimid, king of Cashel, about whom there is more to be said. The Gailings, whose territory lay close by, were loth to be deprived of the customary celebration, and attempted to hold the Assembly on their own account, but were forcibly prevented by the high-king.

In 831, the annals record a disturbance in the courts of the Assembly, owing to some dispute regarding reliquaries of St. Patrick and St. MacCuilinn of Lusk, the reliquaries no doubt being brought there for the purpose of administering oaths in litigation.

Let it not be thought that the silence of the annals in other years is compatible with the absence of the unrecorded event. The entry of the year 873 puts this possibility out of question. It says: "The Assembly of Taillte is not held, in the absence of just and worthy cause, a thing which we have not heard to have befallen from ancient times." Nevertheless, that there was sufficient cause in the disturbed condition of the country owing to the Norse wars is made evident, for the chronicler has to record the abandonment of the Assembly three years later, in 876, when again he denies a just and worthy cause; and again in the second year after that, in 878, without just and worthy cause. When we come to 888, we are told only that the Assembly fell through. This is repeated in 889, and then, when the failure to hold the Assembly becomes annual and, so to speak, normal, the annalist ceases to record it. The next we hear of this institution is in 916, and once more it is the unwonted thing that is chronicled. In that year, the Assembly of Taillte was restored by the high-king, Niall Glúndubh. Hence it would appear that the half-century preceding 916 was the period during which the disturbance of normal conditions in Ireland reached its maximum; and this is also the period of maximum activity for the Norsemen in neighbouring countries.

Aedh Finnliath died in the monastery of Dromiskin in 879. Dromiskin is in Co. Louth, near the sea-coast, and the fact that it was there the high-king "fell asleep," i.e. died a peaceful death in religious retirement, testifies to his success in checking the menace of the Norsemen in northern Ireland. He was succeeded in the monarchy, according to the custom of alternation, by Flann Sinna, king of Meath.