In 1901 Mahler invited Walter to be his assistant at the Court Opera in Vienna. At his first performance he conducted Verdi's "Aida". He was becoming very famous all over Europe. He performed in Prague and in London where in 1910 he conducted "Tristan und Isolde" and Ethel Smyth's "The Wreckers" at Covent Garden. A few months after Mahler's death in 1911, Walter led the first performance of "Das Lied von der Erde" in Munich, as well as Mahler's Symphony No. 9 in Vienna the next year.