Croagh Patrick is an isolated mountain about 2,500 feet (760 meters) above sea level that rises in County Mayo, in the Republic of Ireland. Irish Roman Catholics regard it as a holy mountain because Saint Patrick is said to have spent 40 days in prayer and fasting on its summit, praying for the success of his mission in Ireland. Patrick, who became the patron saint of Ireland, was chiefly responsible for converting the Irish people to Christianity. On the last Sunday of July, thousands of pilgrims climb the mountain to attend Mass in the tiny oratory (room used for prayer).