Grey had landed in Ireland with reinforcements from England to put down the rebellion. His strategy was to meet O'Byrne's threat to the English heartland of Dublin and the Pale by attacking through the highlands to the south of the city. Against the advice of veteran commanders, he chose to lead his army (around 3,000 strong) through lowland Kildare and into the Wicklow Mountains, with the aim of taking the fastness at Balinacor in the Glenmalure Valley.