2 October 1600: The Battle of the Moyry Pass /Cath Bealach na mhaighre on this day. The 'Gap of the North' was the traditional invasion route between Ulster and Leinster going back centuries. It began with a clash of arms between the forces of Aodh O’Neill, Earl of Tyrone and the army of the English Viceroy, Lord Mountjoy. He brought with him some 3,000 foot soldiers and 300 cavalry to try and crush O'Neill's revolt against the English Queen Elizabeth I. The size of O'Neill's force is unknown but was probably in the range of 1,500-2,000 men of all arms.

The battle was initiated by Mountjoy who tried to force his way through the pass west of Newry, which the Irish had fortified. His forces were repulsed with loss and despite repeated attempts over the following days he could not break the Irish lines.

On the 9th he withdrew towards Dundalk. Honour satisfied and with his supplies low the Earl withdrew towards Dungannon. When the English advanced into the Pass that O’Neill had vacated and saw the strength of the defences one wrote that he never saw:' a more villainous piece of work, and an impossible thing for an army to pass without intolerable loss.'. 

Mountjoy then cautiously advanced through the Pass to build Fort Norris and in which he placed a garrison of some 400 men.But Mountjoy knew he could not sustain his stay so deep in Ulster with a full army when Winter was coming and  he withdrew back to Dundalk, not through the Moyry pass (where an ambush was possible), but by way of Carlingford. However O'Neill attacked him anyway when he withdrew and harassed his columns from the woods as they marched by the lough.

The Moyry Pass was not forced. When the campaign was over Mountjoy boasted that he had let the Irish know ‘that their fortifications, though very great, were not the hindrance of our passage’; he claimed that he had been held up not by O’Neill but by bad weather. But he did not move North until O’Neill had got out of his way.

Irish Battles - G.A. Hayes McCoy

However the lateness of the season meant this campaign was now over. O’Neill had done enough to stymie the Viceroy’s attempt to take Dungannon that year and cost the English hundreds of casualties in their futile attempts to take his power base. But Irish losses were heavy too and O'Neill could not so easily replace the expenditure of arms and munitions like Mountjoy was capable of so doing. Tactically he had defeated Mountjoy at the Pass but operationally it at best could be described as a holding measure and strategically it was the case that Mountjoy had gained a foothold inside Ulster ever closer to Dungannon...