Mass for four solo voices, choir, orchestra and organ (D major) op. 123 (Missa solemnis)

One thing was certain for Beethoven: the "Missa Solemnis" was his best composition. It took him a whole four years to complete this monumental work. He negotiated with seven publishers simultaneously when it was finally completed - two years later than planned. Beethoven himself proofread this copy and drew his notes with pencil and red paint.