Most modern writers on Irish history have accepted as historical the romantic story of the cursing of Tara and its desertion during the reign of Diarmait. There is not a word about it in the ancient annals, though our earliest known chronicler wrote within half a century of the supposed event. A son of Diarmait, Aed Sláne, became king of Ireland, and died in 604, within the chronicler's time of writing which ends in 610. Aed Sláne shared the high-kingship with Colmán, king of the Northern Ui Néill, and the chronicle says expressly that "they ruled Tara in equal power." As late as the year 780, Tara was neither an accursed nor a deserted place, for in that year an ecclesiastical synod was held "in the town of Tara" (_in oppido Temro_). The extant stories of the cursing of Tara are all writings of the Middle Irish period, written centuries later than the supposed event. They tell us that the trouble began with the outlawry of Aedh Guaire, king of Ui Maine, who refused to submit to a quite unprecedented exercise of authority on the part of the monarch Diarmait. I have not been able to find this Aedh Guaire's name either in the annals or in the genealogy of Ui Maine, or anywhere except in this story. Aedh Guaire sought sanctuary. Diarmait violated the sanctuary. Twelve saints, called "the twelve apostles of Ireland," thereupon laid siege to Tara with fastings and curses, and Tara ceased to be the home of the monarchy. The annals show that some of these saints were dead at the time and others of them were still in their childhood. These so-called historical tales are seldom troubled about anachronisms. The celebrated "Colloquy with the Ancients" brings St. Patrick and Oisin into conversation with the same Diarmait. Apart from anachronisms, the story of the cursing has other features which should suffice to warn any reader from taking it for serious history. The desertion of Tara does not stand alone, and can be explained without resort to imaginative tales of a later age. Cruachain, the ancient seat of the Connacht kings, and Ailinn, the ancient seat of the Leinster kings, were also abandoned during this period. It was military kings who ruled from these strongholds, surrounded by strong permanent military forces. My first visit to Tara convinced me that what we see there is the remains of a great military encampment. So it appeared or was known to the tenth-century poet Cinaed Ua h-Artacáin, whose poem on Tara begins with the words _Temair Breg_, _baile na fian_, "Tara of Bregia, home of the warrior-bands." When the booty and captives of Britain and Gaul ceased to tempt and recompense a professional soldiery, and when the old fighting castes became gradually merged in the general population, military organisation died out in Ireland, not to reappear until the introduction of the Galloglasses in the thirteenth century. That is one reason why Tara was deserted.