Cheron

From Memory Alpha, the free Star Trek reference.

You may be looking for the Battle of Cheron.

Cheron is a Class M planet located in the southern region of the galaxy near the Coalsack, which once supported a humanoid civilization of Cheron natives. In the 23rd century, the area of space was largely unexplored by Starfleet, so the race was previously unknown to the Federation. (TOS: "Let That Be Your Last Battlefield")