VATICAN CITY (AP) — Thousands of pilgrims are thronging to St. Peter’s Square for the canonization of Mother Teresa, the tiny nun who cared for the world’s most unwanted and became the icon of a Catholic Church that goes to the peripheries to find lost, wounded souls.

Pope Francis is declaring Mother Teresa a saint at a Sunday morning Mass, making her the model of his Jubilee Year of Mercy and in some ways his entire papacy. For Francis, Mother Teresa put into action his ideal for the church to be a merciful “field hospital” for the poorest of the poor — both materially and spiritually.

Throughout the night, pilgrims prayed at vigils in area churches and flocked before dawn to the Vatican under heavy security to try to get a good spot for the Mass that was expected to draw more than 100,000 people.