By May, one of the few remaining garrisons was Tecroghan fort, located on a bog island in County Meath, seven miles west of Trim.
The surrounding terrain was fairly desolate, but the castle was only a few miles from the main Dublin-Athlone road, giving it considerable strategic importance to logistics and trade.
[3][6] In response, the leader of the Royalist alliance, the Duke of Ormond, instructed two of his military commanders, the Earl of Castlehaven and the Marquess of Clanricarde to relieve Tecroghan.
[1][3][7] The allied commanders discussed tactics and agreed that a frontal infantry assault on the siege lines surrounding the castle would be foolhardy because the Parliamentarian cavalry was substantially larger than their small mounted force.
The best way to relieve the garrison, it was agreed, would be to march directly toward the castle as a unit and attempt to break through at a single point.
Such an approach would render the Parliamentarian cavalry virtually useless as the path taken to the castle would be through terrain that would be largely soft, wet bogland.
The Confederate left wing commanded by Colonel Burke attacked the defensive line of the Parliamentarians, broke through, and continued their advance towards the castle.
[3][8] The garrison in the castle, reinforced with what Burke's men were able to carry, did what they could in their own support and began sallying out daily to destroy the defensive works of the English.
[9] Although some authors have considered this a small victory for the Royalist alliance because they broke through to the castle with provisions, the overall plight of the garrison changed very little.