The kingdom of Dál gCais occupied the eastern half of the present county of Clare. Its prominence dates from the time of Lorcán, grandfather of Brian. Being a border state, it was able to form relations of mutual advantage with the border states of Connacht, with Aidne, Ui Maine, and the Delbna. In the wars between Mathgamain and the Limerick Norsemen, the Delbna were his allies. The kings of Aidne and Ui Maine, Connacht states, were allies of Brian, and gave their lives, as he did, on the great day of Clontarf. The killing of Mathgamain in 976 appears in later writings in a more odious light than it could have appeared to contemporaries. We can recognise that the ancient Eoghanacht dynasty of Cashel, which Mathgamain overthrew, had already lost its prestige and was no longer able to rule and protect Munster. It has always happened in the world's history, and is probably happening to-day, that institutions and established powers appear to contemporary people to be full of vigour and likely to last, whereas to people of a later time it is clear that they resembled the hollow tree awaiting the blast that was to lay it low. To the Eoghanacht princes who compassed the death of Mathgamain, he was the successful usurper who had broken into the ancient right of their kindred and held it by the strong hand. With regard to Brian, there are some noteworthy things to be said which even enthusiastic eulogists have ignored. Brian had one or two ideas which, in the Ireland of his time, were revolutionary. He had the idea of a more centralised authority than any Irish king in history before him had attempted to create. To this end, he designed holding in permanent garrison a number of fortified places in various parts of Munster. This design is clearly expressed in a poem added in his time, and no doubt under his direction, to the Book of Rights; and the annals show that he endeavoured to give effect to it.