[1][2][3] The prehistoric royal site of Navan Fort was burnt and plundered and ultimately this territory would re-emerge as part of the kingdom or federation of Airgíalla.

[6][7] The 17th-century historian Geoffrey Keating in his "History of Ireland", in a stylized narrative of events, states: The Collas and the Connaughtmen... marched to the Carn of Achadh leth-derg, in Fernmagh.

The battle of Achadh-leithdheirg, in Fearmhagh, [was fought] by the three Collas against the Ulstermen".... and in a note adds, "This place, situated in the territory of Fearnmagh, now the barony of Farney, in the county of Monaghan, has not been identified.

"[8] A footnote in Lebor na gCeart, published by the Celtic Society in 1847, contains a more expansive commentary regarding the location of Achadh Leith-dheirg: This battle was fought AD332.

When the last great ice caps started receding northwards some ten thousand years ago, Ireland arose once more from a frozen slumber.

Watercourses which are now merely streams were then voluminous torrents, gushing across the land.However between nineteen and thirteen thousand years before the present, during the last glacial period, the ice sheets flowed from Lough Neagh in a south-easterly direction.

Within the bounds of Aghaderg parish are the remains of many sites of great archaeological interest, from stone circles to hill-top forts and settlements along river valleys.

[12] Aghaderg Parish lies within a drumlin belt landscape and encompasses the historic settlements of Loughbrickland and Scarva where King William III encamped.

The two earliest recorded forms of the name Aghaderg - "Uchderc", concerning the site of a battle in AD 1147, between the Ulaid and Cenél nEógain allied with Airgíalla, remain questionable.

[18] Local tradition told that numerous holy men had been killed by the Danes, who destroyed the church and monastery, and that afterwards this place became called Aghdurg, ‘the red or bloody ford’ - the boundary stream running close by the site.

The present county of Monaghan, in the early medieval era was part of the more extensive kingdom of Mugdorna[19][20] - the tribe of Mugdornai: from which the barony of Cremorne derives its name.

As a result, the barony of Farney is today in south Monaghan, many kilometers from where the name began.Livingstone further states: The County's most celebrated crannog [man-made island] was at Lough Ooney, near Smithborough.

[citation needed] Due to Cenél nEógain pressure the Ui Chremthainn power base which had centred on Clogher was shifting south west into Monaghan.

Donnchadh ua Cerbhaill (O'Carroll) endowed the establishment of Mellifont Abbey[28] and under his kingship the airgillia federation would play an immense role in twelfth century developments in Ireland.

In the barony of Dartree, county Monaghan, some five miles south of Clones lies the parish of Currin:[36] through which runs a six-mile remnant of the ancient Black Pig's Dyke or "worm ditch".

This prehistoric fortification of raised earthworks and palisades, on south facing inclines of drumlin hills, has long been regarded as a defensive formation and territorial border.

At the battle of Achaidh Leith-dheirg the forces of the Three Collas had to breach the defences of the Ulaid and this breakthrough must have occurred somewhere along the Fernmhagh-Ulaid border: along the Black Pig's Dyke.

According to Colm Ó Lochlainn an ancient road from Ulster ran south from Tullyhogue Fort and Clogher; then through the Black Pig's Dyke, branching near Cornapaste (townland) Currin parish and on to Belturbet, Ballyconnell and so to Connaught in the west of Ireland.

[40] At a point where the townlands of Aghareagh West and Corrinary meet the earthworks curves into a slight valley before turning abruptly north for some one hundred metres, then continuing east.

The Ulaid would no doubt have been aware of the advance of the Three Collas and although unable to stem the breakthrough at Corrinary, they would have mustered their forces at a very close and advantageous location.