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.

It was now Strongbow’s aim to hasten back and place his new lordship at the feet of his sovereign, already angry and jealous at such unlocked for and uncountenanced successes.  He was not able however to do so at once.  Hasculph the Dane returned suddenly with sixty ships, and a large force under a noted Berserker of the day, known as John the Mad, “warriors,” says Giraldus, “armed in Danish fashion, having long breast-plates and shirts of mail, their shields round and bound about with iron.  They were iron-hearted,” he says, “as well as iron-armed men.”

In spite of their arms and their hearts, he is able triumphantly to proclaim their defeat.  Milo de Cogan, the Norman governor of Dublin, fell upon his assailants suddenly.  John the Mad was slain, as were also nearly all the Berserkers.  Hasculph was brought back in triumph, and promptly beheaded by the conquerors.

He was hardly dead before a new assailant, Godred, king of Man, appeared with thirty ships at the mouth of the Liffy.  Roderick, in the meanwhile, had collected men from every part of Ireland, with the exception of the north which stood aloof from him, and now laid siege to Dublin by land, helped by St. Lawrence its patriotic archbishop.  Strongbow was thus shut in with foes behind and before, and the like disaster had befallen Robert FitzStephen, who was at this time closely besieged in his own new castle at Wexford.  Dermot their chief native ally had recently died.  There seemed for a while a reasonable chance that the invaders would be driven back and pushed bodily into the sea.

Discipline and science however again prevailed.  The besieged, excited both by their own danger and that of their friends in the south, made a desperate sally.  The Irish army kept no watch, and was absolutely undrilled.  A panic set in.  The besiegers fled, leaving behind them their stores of provisions, and the conquerors thereupon marched away in triumph to the relief of FitzStephen.  Here they were less successful.  By force, or according to Giraldus, by a pretended tale of the destruction of all the other invaders, the Wexford men seized possession of him and the other English, and had them flung into a dungeon.  Finding that Strongbow and the rest were not destroyed, but that on the contrary they were marching down on them, the Wexford men set fire to their own town and departed to an island in the harbour, carrying their prisoner with them and threatening if pursued to cut off his head.