How did Saint Patrick become a saint?

Saint Patrick was never canonized by the Catholic Church, but people and churches all around the world view him as a saint for his missionary work. He died on March 17, 460. The date of his death is called Saint Patrick's Day in his honor.

Saint Patrick worked to spread Christianity to Ireland. He was captured by Irish pirates at 16, but he escaped. His experience inspired him to go back to Ireland as a priest. The Pope consecrated Saint Patrick as Bishop of the Irish in 431. Saint Patrick later invented the Celtic cross, a combination of Christian and pagan symbols.