Posthorn

The post horn is a valveless cylindrical brass
instrument with a cupped mouthpiece.
The instrument was used to signal the arrival
or departure of a post rider or mail coach, and
was used especially by postilions of the 18th
and 19th centuries. The post horn was used
in the famous off-stage solo in Mahler's
Symphony No. 3. The sound of the instrument
has been substituted by the trumpet, cornet or
flugelhorn.