The division already existed before the symphony. String quartets, which date back to the 1500s, also have two violins, one viola, and one cello. Before that arrangement became standardized, there were different instrumentations for string quartets. Some of the sixteenth century music, like Pachelbel's Cannon in D, was originally written for three violins and continuo. The continuo was replaced by the cello, and the viola replaced the third violin. There was also quartet music written for the viol family instead of the violin family. Before we had symphonies, we had chamber orchestras. The symphony orchestra is simply an expansion of the chamber orchestra instrumentation. The symphony also went through a period of standardization. There are orchestra pieces that have no parts for some of the instruments, and they either sit that piece out during concerts, or they double the part of another instrument. The first thing you must understand if you are going to study music history is that in most cases there is no decision point for our musical traditions and no invention of our instruments. Most things, with a few notable exceptions like the saxophone, came about because there were other ideas that were less popular among musicians or instruments composers were not using, so slow changes were made to make the instruments that remained accommodate the music that remained.