Nevertheless, fugues did not take on a truly central role in Beethoven's work until his late period. The finale of Beethoven's "Hammerklavier" Sonata contains a fugue, which was practically unperformed until the late 19th century, due to its tremendous technical difficulty and length. The last movement of his Cello Sonata, Op. 102 No. 2 is a fugue, and there are fugal passages in the last movements of his Piano Sonatas in A major, Op. 101 and A major Op. 110. According to Charles Rosen (1971, p. 503) "With the finale of 110, Beethoven re-conceived the significance of the most traditional elements of fugue writing."