Although his symphonies, concertos and choral music are now internationally acclaimed, Nielsen's career and personal life were marked by many difficulties, often reflected in his music. The works he composed between 1897 and 1904 are sometimes ascribed to his "psychological" period, resulting mainly from a turbulent marriage with the sculptor Anne Marie Brodersen. Nielsen is especially noted for his six symphonies, his Wind Quintet and his concertos for violin, flute and clarinet. In Denmark, his opera "Maskarade" and many of his songs have become an integral part of the national heritage. His early music was inspired by composers such as Brahms and Grieg, but he soon developed his own style, first experimenting with progressive tonality and later diverging even more radically from the standards of composition still common at the time. Nielsen's sixth and final symphony, "Sinfonia semplice", was written in 1924–25. He died from a heart attack six years later, and is buried in Vestre Cemetery, Copenhagen.