Between Ulster and North Leinster, the boundary ran from Loch Bóderg on the Shannon through the southern part of County Leitrim, and thence in the direction of Granard; thence by the present boundary of Ulster eastward as far as the Blackwater, down along the Blackwater to Navan and from Navan along the Boyne to the Irish Sea. On the expedition of the Táin, Medb's army skirted this boundary, keeping on the Leinster side, until they reached the Blackwater; and the story tells how they looked across the Blackwater at "the foreign territory" (_in chrich aineoil_). Such was the division of Ireland under the Pentarchy at the beginning of the Christian Era, as disclosed by the oldest traditions. When we come to St. Patrick's time, the fifth century, we feel ourselves within the scope of clear and definite written records. These ancient boundaries are for the most part only memories. There is no longer a Pentarchy but a Heptarchy, which remains substantially unchanged for several centuries and is described in detail by the Book of Rights, compiled about the year 900 and revised about a century later. In this new arrangement, Munster has its present extent plus the southern angle of King's County. Connacht has lost County Clare, but has annexed territory east of the Shannon as far as Loch Erne and Loch Ramor in County Cavan. This territory has been taken from Ulster, which no longer exists as a political unit, but is divided into three of the seven chief kingdoms. These are the kingdom of Ailech on the west, the kingdom of Ulaidh on the east, and the kingdom of Airgialla or Oriel in the middle. The Fifth of North Leinster has ceased to be a kingdom. There is only one kingdom of Leinster, which extends as far north as Dublin, the river Liffey and its tributary the Rye, which runs by Maynooth. This kingdom contains what remains of North and South Leinster and is ruled by the ancient dynasty of South Leinster. The seventh chief realm is that of Meath which has been formed from parts of North Leinster and of Ulster. Its northern boundary is nearly but not quite the same as the present northern boundary of Leinster. It takes in part of County Cavan and excludes the northern part of County Louth, north of Ardee. The strictly historical period in Ireland begins with St. Patrick. The authentic writings of St. Patrick are the earliest written documents of Irish history. But I do not think it would be just to say that all before that time is prehistoric. If all we had for the first four centuries of the Christian Era was a slender thread of narrative like Livy's story of ancient Rome, we might wonder how much profit, if any, could come from examining it. We are not in so poor a case. We have a substantial mass of traditions, connected and disconnected, which, I think, enable us to supply the void of written documents in a manner that will carry conviction.