(Latin: “Day of Wrath”), the opening words of a Latin hymn on the Last Judgment, ascribed to Thomas of Celano (d. c. 1256) and once forming part of the office for the dead and requiem mass.

The hymn ascribed to Thomas of Celano contains 18 rhymed stanzas (17 tercets, 1 quatrain), to which a later, anonymous writer added an unrhymed couplet, ending in “Amen.” The impressive plainsong melody to which the hymn was sung was used by composers of religious works from the 16th century onward, either in its original form or as the basis of a polyphonic composition. Wolfgang Amadeus Mozart and Giuseppi Verdi were among the composers of religious works who wrote original music on the text of the hymn.

The original melody had strong appeal during the Romantic period and was used, often in the form of a parody or to suggest the supernatural or the macabre, in many secular compositions by Hector Berlioz, Camille Saint-Saëns, Ralph Vaughan Williams, and other composers.