Brian was now undisputed King of Munster. In 984 he was acknowledged Monarch of Leth Mogha, the southern half of Ireland. Meanwhile Malachy, who governed Leth Cuinn, or the northern half of Ireland, had not been idle. He fought a battle with the Danes in 979, near Tara, in which he defeated their forces, and slew Raguall, son of Amlaibh, King of Dublin. Amlaibh felt the defeat so severely, that he retired to Iona, where he died of a broken heart. Donough O'Neill, son of Muircheartach, died this year, and Malachy obtained the regal dignity. Emboldened by his success at Tara, he resolved to attack the foreigners in Dublin; he therefore laid siege to that city, and compelled it to surrender after three days, liberated two thousand prisoners, including the King of Leinster, and took abundant spoils. At the same time he issued a proclamation, freeing every Irishman then in bondage to the Danes, and stipulating that the race of Nial should henceforth be free from tribute to the foreigners. It is probable that Brian had already formed designs for obtaining the royal power. The country resounded with the fame of his exploits, and Malachy became aware at last that he should either have him for an ally or an enemy. He prudently chose the former alternative, and in the nineteenth year of his reign (997 according to the Four Masters) he made arrangements with Brian for a great campaign against the common enemy. Malachy surrendered all hostages to Brian, and Brian agreed to recognize Malachy as sole Monarch of northern Erinn, "without war or trespass." This treaty was absolutely necessary, in order to offer effective resistance to the Danes. The conduct of the two kings towards each other had not been of a conciliatory nature previously. In 981 Malachy had invaded the territory of the Dalcassians, and uprooted the great oak-tree of Magh Adair, under which its kings were crowned--an insult which could not fail to excite bitter feelings both in prince and people. In 989 the monarch occupied himself fighting the Danes in Dublin, to whom he laid siege for twenty nights, reducing the garrison to such straits that they were obliged to drink the salt water when the tide rose in the river. Brian then made reprisals on Malachy, by sending boats up the Shannon burning the royal rath of Dun Sciath. Malachy, in his turn, recrossed the Shannon, burned Nenagh, plundered Ormonde, and defeated Brian himself in battle. He then marched again to Dublin, and once more attacked "the proud invader." It was on this occasion that he obtained the "collar of gold," which Moore has immortalized in his world-famous "Melodies."