His purpose achieved, "inflamed," says Giraldus, "with the desire to see his native land," but really the better to concoct his plans, he returned home, landing a little south of Arklow Head, and arriving at Ferns, where he was hospitably entertained during the winter by its bishop. The following spring, in the month of May, the first instalment of the invaders arrived under Robert FitzStephen, a small fleet of Welsh boats landing them in a creek of the bay of Bannow, where a chasm between the rocks was long known as "FitzStephen's stride."
Here they were met by Donald McMurrough, son of Dermot, and ten days later drew up under the walls of Wexford, having so far encountered no opposition.
In this old Danish town a stout fight was made. The townsfolk, no longer Vikings but simple traders, did what they could in their own defence. They burnt their suburbs, consisting doubtless of rude wooden huts; shut the gates, and upon the first two assaults drove back the assailants. So violently were they repelled, "that they withdrew," Giraldus tells us, "in all great haste from the walls." His own younger brother, Robert de Barri, was amongst the wounded, a great stone falling upon his helmet and tumbling him headlong into one of the ditches, from the effects of which blow, that careful historian informs us incidentally, "Sixteen years later all his jaw teeth fell out!"
Next morning, after mass, they renewed the assault; this time with more circumspection. Now there were at that time, as it happened, two bishops in the town, who devoted their energies to endeavouring to induce the citizens to make peace. In this attempt they were successful, more successful than might have been expected with men descended from the old Land Leapers. Wexford opened its gates, its townsmen submitting to Dermot, who thereupon presented the town to his allies, FitzStephen, true to his Norman instincts, proceeding forthwith to build a castle upon the rock of Carneg, at the narrowest point of the river Slaney, the first of that large crop of castles which subsequently sprang up upon Irish soil.
The next sharers of the struggle were the wild Ossory clans, who gathered to the defence of their territory under Donough McPatrick, an old and especially hated enemy of Dermot's. The latter had now three thousand men at his back, in addition to his Welsh and Norman allies. The Ossory men fought, as Giraldus admits, with furious valour, but upon rashly venturing out of their own forests into the open, were charged by FitzStephen, whose horsemen defeated them, killing a great number, over two hundred heads being collected and laid at the feet of Dermot, who, "turning them over, one by one, to recognize them, lifted his hands to heaven in excess of joy, and with a loud voice returned thanks to God most High." So pious was Dermot!
After this, finding that the country at large was beginning to take some note of their proceedings, the invaders fell back upon Ferns, which they fortified according to the science of the age under the superintendence of Robert FitzStephen. Roderick O'Connor, the Ard-Reagh, was by this time not unnaturally beginning to get alarmed, and had gathered his men together against the invaders. The winter, however, was now at hand, and a temporary peace was accordingly patched up; Leinster being restored to Dermot on condition of his acknowledging the over-lordship of Roderick. Giraldus recounts at much length the speeches made upon both sides on this occasion; the martial addresses to the troops, the many classical and flowery quotations, which last he is good enough to bestow upon the unlucky Roderick no less than upon his own allies. Seeing, probably, that all were alike imaginary, it is hardly necessary to delay to record them.
The next to arrive upon the scene was Maurice Fitzgerald, half brother of Robert FitzStephen and uncle of Giraldus. Strongbow meanwhile was still upon the eastern side of the channel awaiting the return of his uncle, Hervey de Montmorency, whom he had sent over to report upon the condition of affairs. Even after Hervey's return bringing with him a favourable report, he had still the king's permission to gain. Early in 1170 he again sought Henry and this time received an ambiguous reply, which, however, he chose to interpret in his own favour. He sent back Hervey to Ireland, accompanied by Raymond Fitzgerald, surnamed Le Gros, and a score of knights with some seventy archers. These, landing in Kilkenny, entrenched themselves, and being shortly afterwards attacked by the Danes of Waterford, defeated them with great slaughter, seizing a number of prisoners. Over these prisoners a dispute arose; Raymond was for sparing their lives, Hervey de Montmorency for slaying. The eloquence of the latter prevailed. "The citizens," says Giraldus, "as men condemned, had their limbs broken and were cast headlong into the sea and so drowned."
Shortly after this satisfactory beginning, Strongbow himself appeared with reinforcements. He attacked Waterford, which was taken after a short but furious resistance, and the united forces of Dermot and the Earl marched into the town, where the marriage of the latter with Eva, Dermot's daughter, was celebrated, as Maclise has represented it in his picture, amid lowering smoke and heaps of the dead and dying.
Dermot was now on the top of the wave. With his English allies and his own followers he had a considerable force around him. Guiding the latter through the Wicklow mountains, which they would probably have hardly got through unaided, he descended with them upon Dublin, and despite the efforts of St. Lawrence O'Toole, its archbishop, to effect a pacific arrangement, the town was taken by assault. The principal Danes, with Hasculph, their Danish governor, escaped to their ships and sailed hastily away for the Orkneys.
Meath was the next point to be attacked. O'Rorke, the old foe of Dermot, who held it for King Roderick, was defeated; whereupon, in defiance of his previous promises, Dermot threw off all disguise and proclaimed himself king of Ireland, upon which Roderick, as the only retaliation left in his power, slew Dermot's son who had been deposited in his hands as hostage.