Klaus Mertens and consistency, Klaus Mertens sang in every piece that required a bass soloist, 190 in all." He is also involved in the project Dieterich Buxtehude – Opera Omnia of the same ensemble to record the complete works of Dieterich Buxtehude, begun in 2005. As a singer of lieder, he has interpreted songs of Claudio Monteverdi, Antonio Caldara, Wolfgang Amadeus Mozart and Franz Schubert among others. He has performed the title roles of the romantic oratorios "Elijah" and "St. Paul" by Mendelssohn and, as music of the 20th century, Paul Hindemith's "Requiem" and Igor Stravinsky's "Oedipus rex". In the classical repertory
Christus. Mysterium in a Prelude and Three Oratorios International Draeseke Society, he played them in the town church of Coburg. Christus is composed of four separate sections: Though the work is composed of three oratorios, it bears more resemblance to Wagner's "Ring Cycle" than to traditional oratorio. Draeseke intended for it to fit into the category of Wagner's "Musikdrama," and in fact he used leitmotif throughout the work. Because of its length, a performance of "Christus" spans three evenings. The work was only performed twice in its entirety and, unlike Wagner's "Ring Cycle", Draeseke preferred that his work be performed in a church. Draeseke wrote in program notes