- You may be looking for the Battle of Cheron.
Cheron was an uninhabited planet in the 23rd century. It was the homeworld of the Cheron natives, an extinct warp capable humanoid species. The planet was located in the southern region of the Milky Way Galaxy near the Coalsack Nebula.
History
Prior to stardate 5730, this planet and its inhabitants were unknown to the United Federation of Planets. In 2268, first contact was made with this planet's inhabitants.
In that year, when the USS Enterprise scanned the planet, the instruments revealed large uninhabited cities, extensive traffic systems barren of traffic, and lower animal lifeforms and sand encroaching on the cities. There was no sign of sapient life, and there were vast numbers of unburied corpses in the cites. The civilization had evidently destroyed itself in a war fueled by racism. The last two surviving members of the species, Bele and Lokai, were left behind on this world by the Enterprise. (TOS: "Let That Be Your Last Battlefield")
The location of Cheron was labeled in the star chart Data and Picard were studying in stellar cartography in 2371. (Star Trek Generations display graphic)
Appendices
Background information
According to the Star Trek: Star Charts (pgs. 60 and 66), Cheron was located in the 83 Leonis system in the Beta Quadrant. 83 Leonis was listed as a single star system with a K class primary with a magnitude lower than Sol. In the mid-22nd century, the 83 Leonis system was located in non-aligned space. In 2378, the system was located in or near Federation space.
According to the reference book Star Trek: Federation - The First 150 Years, Cheron was the planet where the Battle of Cheron of the Earth-Romulan War took place.
Apocrypha
According to the novels The Buried Age, Kobayashi Maru and To Brave the Storm, the planet Cheron was the fifth planet in the 83 Leonis B star system, and was the site of the Battle of Cheron in 2160. Cheron was a strategically important planet for the Romulan Star Empire and was occupied with a military outpost at the time. Cheron was also where a Romulan fleet of 81 ships massed in preparations for an all out attack on Earth. The fleet was defeated and forced to retreat by allied starships. After the war, Cheron remained on the Federation side of the Romulan Neutral Zone.