The Missa solemnis in D major, Op. 123, is a Solemn Mass composed by Ludwig van Beethoven from 1819 to 1823. It was first performed on 7 April 1824 in Saint Petersburg, Russia, under the auspices of Beethoven's patron Prince Nikolai Galitzin; an incomplete performance was given in Vienna on 7 May 1824, when the Kyrie, Credo, and Agnus Dei were conducted by the composer. It is generally considered one of the composer's supreme achievements and, along with Bach's Mass in B minor, one of the most significant Mass settings of the common practice period.