The rebel lookout on the peak of Lugnaquilla sounded the alarm, and Grey ordered his men to descend into the glen with a drum roll. O'Byrne had concealed his men in the craggy terrain, and the English troops, conspicuous in their red and blue coats and white hose, instantly found themselves sliding along a river course. Decimated by sniping gunfire, they hit bottom fully a mile in depth from the point where the glen was entered. The Irish did not wait: shots were fired from both sides, and the kern descended to engage in hand-to-hand combat. Grey's troops were routed with the loss of hundreds, and much valuable equipment had to be discarded. Grey spurred his cavalry on to check the pursuit and force the rebels back into the glen, but even on the retreat to Dublin the punishment was withering.