When twenty-six-year-old Mozart was married to his wife Constanze, he promised her that he would write her a grand mass in honor of the occasion. The promise remained (mostly) unfulfilled until his death; he completed only half of the work, and so it is left to scholars to imagine what might have been. Nonetheless, it is one of Mozart’s most startlingly beautiful works, and Collegium will perform it in a completion by the scholar Frieder Bernius. Scored for a double chorus and an orchestra complete with trombones and timpani, Mozart’s Mass in C Minor is a piece for the ages!