Missa in D "Missa brevis"

The celebration of the Mass is at the heart of Roman Catholic liturgy. Musical settings of the Ordinarium Missae consist of the Kyrie, Gloria, Credo, Sanctus (with Osanna), Benedictus (with Osanna), and Agnus Dei. In Salzburg, a differentiated system existed to determine what kind of settings were required for which celebrations. Some of Mozart's earliest Masses were composed for special occasions such as priestly or church consecrations. After his appointment as concertmaster, Mozart regularly composed music for Salzburg Cathedral and was the most productive composer of church music there during the 1770s. The use of trumpets and timpani indicates that most of his settings were intended for feast days on which the Prince-Archbishop himself celebrated the Mass. Typically, Masses in southern Germany and Austria do not include viola parts. After moving to Vienna, Mozart never held another ecclesiastical office; nevertheless, he began composing several Masses there, though he completed none of them. In April 1791, Mozart's request to substitute for the ailing Kapellmeister of St. Stephen's Cathedral in Vienna, Leopold Hofmann, was approved, but he did not live long enough to actually succeed him. The Requiem, as a Mass for the dead, uses a special form of the Missale Romanum. In Salzburg and Vienna, Requiem settings were composed only for special occasions.