The term DIES IRAE (4 letters) is a Latin hymn which translates to 'Day of Wrath'. It is a medieval poem which is often used as part of the Requiem Mass in the Roman Catholic Church. It is believed to have been written by Thomas of Celano in the 13th century and is composed of 18 verses. The poem is a reflection on the Last Judgment and the Day of Wrath when God will come to judge the living and the dead.