An extinct people who fought a war against the Menthars a thousand years ago and left behind a battle cruiser caught in an ancient trap.
The Promellians were an ancient spacefaring people who waged a long war against the Menthars around a thousand years ago. Both species are believed to have perished in that conflict, and the region where they fought is still littered with wreckage.
In the episode Booby Trap, the Enterprise-D found an intact Promellian battle cruiser near Orelious IX and soon became caught in the same Menthar trap that had killed its crew: a field of devices that drained a ship's energy and turned it into deadly radiation. Geordi La Forge worked with a holodeck simulation of Dr. Leah Brahms to find a solution, and Captain Picard finally piloted the ship out manually.