Mar Mattai houses the tomb of Mor Mattai beneath the altar in the Main Church of St. Matthew, along with the burial vaults of historic maphrians and medieval church leaders. The monastery library also preserves over 200 rare Syriac manuscripts, including a historic New Testament manuscript copied in 1222 AD. For more: Christian Heritage in Northern Iraq: A Guide to Alqosh, Mar Mattai, and the Nineveh Plains