Until recently, little was known about trombone repertoire from the 18th century. In recent years, the discovery of new repertoire and emerging information regarding the Austrian alto trombone virtuoso Thomas Gschladt demonstrates that the alto trombone enjoyed a period of prosperity between 1756 and 1780. In the 1960s an incomplete concerto by Georg Christoph Wagenseil was recorded by conductor Nikolaus Harnoncourt: this Concerto demands advanced technique from the performer and is the first known concerto form work for the trombone. Shortly after this recording was released, another concerto, written by Leopold Mozart was discovered. But due to the advanced technique required in this concerto (particularly the lip trills), it was considered too difficult for the trombone and musicologists concluded that it was instead most likely written for the French horn. New information regarding Gschladt demonstrates that music of this difficulty was written for the alto trombone during the mid-to-late 18th century and that music we previously thought impossible on the instrument was certainly possible. Like Bach's trumpet soloist Gottfried Reiche and Mozart's horn soloist, Joseph Leutgeb, Gschladt then represented the best of contemporary trombone soloists. Gschladt was very close to Leopold Mozart who wrote a Serenade especially to be performed only by him, and when Gschladt was unavailable, Mozart preferred using a viola soloist over another trombonist.