Domenico Sarro - Sinfonia from the opera Achille in Sciro

The Real Teatro di San Carlo in Naples is the oldest opera house in the world that is still in use.  It was inaugurated on this day in 1737, and this was the very first music performed there.

View from the Royal box.  Image from Il Wik

Domenico Sarro was one of the most important composers of Neapolitan opera in the 18th century, an era when it enjoyed popularity all over Europe.  His reputation was such that his work was chosen to inaugurate the new opera house, in a command performance before the King.  His relative obscurity today can be chalked up to changing musical tastes (and particularly the fading of both baroque and opera in favor of romantic era symphonies).  But at the time this stood equal to Handel and Bach.