Overtures (known in German as 'Vorspiel') are pieces originally meant to function as an instrumental introduction to an opera. They have their roots in the first operas, which opened with brief fanfares as a way of calling the attention of the audience. A musical form called 'ouverture' can be found in early French ballet, featuring a slow introduction followed by a lively section. This form would eventually make its way to the works of Johann Sebastian Bach. Also, another distinct form called 'overture' arose in Italy at the end of the 17th century, consisting of three sections in a fast-slow-fast sequence. Both forms would later influence the symphony.
By the end of the 18th century, overtures were already beginning to be performed as separate pieces in concerts. This gave birth to the concert overture, a standalone form of music, usually based on a literary theme. This was the vehicle chosen by many post-Beethovenian composers to avoid the symphonic form. The concert overture was eventually replaced by the symphonic poem.