In the early morning of 23rd August, Humbert sent a
reconnaissance party under Col Sarrizen to Ballina. Close to the town he realised that the garrison of 600 Fensibles was far larger than his own party and returned to Killala. Seeing this as a retreat, the Crown Forces marched on Killala that night and were outflanked by a surprise Franco/Irish force near Rosserk Friary. They fell back to Ballina, evacuated the town and retreated to Foxford before dawn. The French camped for the night near Rosserk Abbey and the following morning entered Ballina  unopposed. Locals lit fires of straw along the route to guide the French and Irish Rebels---The road is now known as "Bother-na-sop" or the road of the straws.
         Humbert who was still in Killala moved into Ballina taking hostages (including Bishop Stock's son) to protect his provisions in Killala. News spread quickly and many more Irish rebels joined Humbert. Bartholomew Teeling, an Irish colonel in the French army, was placed in command of the "Legion" - 500 Irish rebels who were regarded by the French as the best soldiers.
Humbert set up headquarters in the house of Colonel King and started to plan his attack on Castlebar. A Fr. Conroy suggested that Humbert should enter Castlebar through a little known mountain pass from Larhadane. It was decided to take this advice as it would give the attacking forces the element of surprise.
       On the afternoon of the 26th. August General Humbert set out, with his French/Irish army , to take Castlebar.