The Lebor Gabála Érenn is the Middle Irish title, Taking of Ireland, the book catalogues the path of the Gaels' ancestors in a way that, an account of the creation of the world down to the Middle Ages, as well as actual historical events from discovery of a form of early Ogham script in Celtic Gallaecia, as well as genetic studies linking the Gaels to the Basques and Galicians in northwestern Spain. From the fall of Akkad until around 2100 BC and the Ninth Dynasty wars in Egypt; Magh Ithe, first recorded battle in Ireland myths (2071 BC).

In the 3rd century, Diocletian created an administrative division which included the conventus of Gallaecia, Asturica and perhaps Cluniense. It is usually known in English as The Book of Invasions or The Book of Conquests.

Magh Ithe, the "Plain of Ith", was said to have been named after Ith, the uncle of Míl Espáine, who was killed by the Tuatha Dé Danann. It was located between Lough Foyle, Lough Swilly and the River Finn in Counties Donegal and Londonderry. The Ulster Cycle, formerly the Red Branch Cycle of Emain Macha, centres around the reign of Conchobar mac Nessa, who is said to have been king of Ulster around the time of Christ. Traditions of the Turkic Kazakhs and Yakuts (who call themselves "Sakha"); the Marathas of India; the Picts; the Gaels; the Hungarians; Serbs and Croats (among others) also include mention of Scythian origins of the Greek Dark Ages. The Sarmatians and Scythians of Eurasia by the time of the Byzantine Empire, placed a notion of some of the Scythians and the Huns being of Scythian ancestry and the name of the land of Scythian origin as Gerrhos meaning swamp of reeds, which is on the meridian of the Eastern Axis of Egypt according to Hebrew Exodus. Written records of the ancient Egyptian language have been dated from about 3200 BC.

The North Albans or Picts (Cruithne) of historical times were divided into great northern and southern tribal kingdoms. This tribe quickly assimilated or destroyed the original Old European inhabitants of the Bronze Age, of the north of the British island. Around 8000 BC, during the Mesolithic or Middle Stone Age, settlers arrived from the Balkans in North Antrim with the core area of the kingdom ran from the River Bush in the west, south to Glenravel. The most likely site of the capital of Dalriada was Dunseverick in County Antrim. Dalriada was named for the clan known as the Dál Riata whose origins were in the coastal region of north-east Antrim.

The more ancient Pictish tribal partition described in the second century by Ptolemy is thirteen-fold, and includes the Caledonians themselves as the chief tribe of the North, their territory being roughly equivalent to north-central Scotland above Dunkeld (the fort of the Caledonians) in Perthshire. The physical empire of the Romans separated the unruly Selgovae tribe in the north from the Brigantes in the south and discourage them from uniting. Ireland was known to the Romans as Scotia; what is modern Scotland, was called Alba and was home to the Picts. As a result of settlement on the west coast of Alba by the Scoti of Fermanagh, the area became known as Scotia Minor. Alba claimed the name Scotia; Land of the Scoti, to itself.

The first settlers from the Irish tribe of Dal Riata in County Antrim arrived in Argyll around 400 AD. The Cineal nAlbanaich were a branch of the Laigin and Oirghialla that settled in the northwest Highlands and Islands in very early times. By 400 AD, Irish Scots raid and settle in (Wessex) Wales, Devon and Cornwall. Three British kingdoms are established north of Hadrian's Wall: Strathclyde, Gododdin and Galloway. This is a period of prosperity in south-east Britain, but the towns remain garrisoned, mainly by auxiliary troops. Christianity extends to kingdoms north of Hadrian's Wall and to southern Ireland. The Luighne were of County Sligo, where they had settled as fighting men to the Northern Gaels in the early centuries A.D. The Cianacht were closely related to the Dealbhna and Saithne.

Niall of the Nine Hostages, the high king of Ireland, leads raids on Britain's south coast while German tribes, crossing the ice-bound Rhine, overrun Gaul. The withdrawal of the last Roman legions after 406 AD, opened the way for waves of Pictish raiders to swoop down on the now largely Romanized Britons in the south. In 503 or 506 AD when the three sons of Erc, Fergus, Aengus and Loarn, seized power in Scotland. The area they colonised subsequently became known as Airrer Gaedhil, the territory of the Gael – modern-day Argyll. The Scots of Dalriada were originally from Ireland, from an area along the Antrim coast and part of the province of Ulster (now counties Antrim and Down). The originator of the political territory of the Dál Riata in Scotland was Fergus Mór mac Eirc who arrived in Kintyre c. 500.

The Dal nAraidhe tribe is the historical representative of the ancient Picts of Ulster. Although the kings of Dál Fiatach were usually located south of the Lagan in modern Co. Down, there were occasions in which they had their headquarters north of the river. For six centuries, therefore, the King of Emania was Sovereign of all Ulster and sometimes also High-King of Leland. The three Collas made war upon the Ulster King, plundered his territory, and burned the palace, around which centred the romantic tales of the Red Branch Knights. The Ulidians were driven eastwards over Glenree, or the Newry River. From this time onward the term Ulidia, or Uladh, is applied to the tract of country lying to the east of Lough Neagh and the Newry River. Sometimes the Plain of Muirtheimhne, or North Louth, was included. Crích Ross stands 4 miles northewet of the point where counites Monaghan, Louth and Meath meet. The Cenél n-Enda mic Neill were noted west of Loch Erne (Book of Lecan).

The Uí Tuirtre of South Derry moved eastward across the River Bann as their lands were absorbed into the expanding Uí Neill over-kingdom of Cenél Eoghain in the eighth century and was within the traditional territory of the Uí Thuirtre, Airtheara, and Fir Lí, west of the Bann. East of the Bann, the Uí Tuirtre were allies of the Dal nAraidi. The territory of the Uí Tuitre was also said to have included an area west of Lough Neagh (in modern co. Tyrone), as well as northwest of the great Lough in the modern barony of Loughinsholin, co, Derry. In the early Middle Ages, the tribe sometimes held the over-kingship of Ulaid, roughly eastern Ulster, alternating it with the north and west branch chief clan of the Ulster Erainn. The Ui Eachach Cobha, a branch of the Dal nAraidhe, gave rise to the Clan Aodha (Antrim, Derry, Fermanagh) and the Cenél Faghartaigh and the Loigis were commonly referred to as the "Seven Septs of Leix." The Leabhar na gCeart cites the people of Ara (Arada, Aradh) were Rudricians, descended from Feartlachta, son of Fearghus, King of Ulster, in the 1st century.

Around the end of 6th Century, a wave of Irish Celts, called the Scots, invaded the territory from across the Irish Sea. This new wave of Celts soon dominated the entire region to the point where they became synonymous with the land to which they gave their name - Scotland. Soon after the arrival of the Angles and the Saxons, the southern most part of the Pictish lands was overrun by the new invaders: it became the kingdom of Northumbria. The Irish immigrants (the Scots) settled in the west in Dalriada (around Argyll). Wales was then divided up into several tribal areas, including Gwynedd, Gwent, Dyved and Powys. King Aidan of Dalriada attempted to extend the boundaries of his realm to the east across central Scotland but the Northumbrian King Aethelfrith defeated him at the battle of Degsastan around 603.

The period after Domhnall Brecc's death in 642 at the hands of Owen king of Strathclyde, marked the beginnings of a decline of Dalriada and also Iona. Iona suffered a setback of huge proportions at the Synod of Whitby over the date of Easter and the tonsure. In 685, Pictish lands north of the Firth of Forth sea inlet were invaded by a large Northumbrian army. The invaders were however dramatically defeated, leading to a weakening of the kingdom of Northumbria from which they never recovered. As a result, even larger areas of northern England were occupied by the Picts. By the end of the seventh century the military failures at Fortriu that had befallen the Cenél nGabráin allowed a fourth kindred to emerge: the Cenél Comgaill, while they themselves were replaced as kings of Dalriada by the Cenél Loairn. The power of the Cenél Loairn was eclipsed less than a hundred years later by the rise of Pictish power in the east of Dalriada in 741. A century after a century the king of the Cenél Loairn would become king of the Picts and unite the two nations into one, Alba.