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Rowan University: Matthias the Apostle
This short article deals with the story of St. Matthias, the "13th. Apostle", chosen by the others to replace Judas after his death. This site also contains prayers in his honor.
New Advent
Catholic Encyclopedia: St. Matthias
This article looks at the calling of St. Matthias as the "replacement" apostle. He was chosen to replace Judas Iscariot to return the number of apostles to twelve. Please note that ?The Catholic Encyclopedia? is a historic reference...