kings, queens and nobility, the children could converse in several languages; the tour represented, for them, an outstanding education. However, these advantages had been gained at a price; Grimm, in Paris, noting the stress and strain on Wolfgang in particular, had feared that "so premature a fruit might fall before maturing". However, Hildesheimer, while also expressing concerns, concludes that if Mozart's death at the age of 35 was caused by the exertions of his childhood, the intervening decades would not have been so productive, and obvious symptoms of decline would have manifested themselves. Of Wolfgang's music composed during the tour, around thirty pieces survive. A number of works are lost, including the Zürich cello pieces and several symphonies. The surviving works include the keyboard sonatas written in Paris, London and The Hague, four symphonies, various arias, the assorted music written for the Prince of Orange, a Kyrie, and other minor pieces. Mozart's career as a symphonist began in London where, in addition to the direct influences of Abel and J.C. Bach, he would have heard symphonies from leading London composers including Thomas Arne, William Boyce and Giuseppe Sammartini—"a nearly ideal introduction to the genre", according to Zaslaw. The earliest symphonies, Zaslaw points out, while not in the same class as the later Mozart masterpieces, are comparable in length, complexity and originality to those written at the same time by the acknowledged symphonic masters of the day. Indeed, Abel's Symphony No. 6 in E Flat was similar enough in style and technique to be mistaken as Mozart's, and is listed as such (Symphony No. 3, K. 18) in the original Köchel catalogue. Sadie observes that the K. 22 symphony composed in The Hague is a good deal more sophisticated than the earlier ones which were written in London. Mozart's creative progress is likewise reflected in the sonatas composed for the Princess of Orange, which, according to Sadie, mark a considerable advance in technique and ideas over the earlier Paris and London sets. The arias composed in the Netherlands include Mozart's first attempts at "aria d'affetto", Per pièta, bell'idol mio, K. 73b, once thought to have been composed much later, as its higher K number indicates. The tour thus saw Wolfgang's transformation from a composer of simple keyboard pieces to one with increasing mastery over a range of genres. This was evidenced in his home city, on 8 December, when one of