The Battle of Orelious IX was a battle that took place on the planet Orelious IX between the Promellians and Menthars.
Despite the fact that neither side expected a large battle, it was the last and decisive one between the two species and lead to their mutual extinction during the 14th century. It also resulted in the planet's destruction.
The USS Enterprise-D underwent a mission from the United Federation of Planets in 2366 to chart the battle. Remnants of a Menthar booby trap temporarily held it inside the asteroid field. (TNG: "Booby Trap")