A planet where a worn-out Starfleet garrison defends a captured Dominion communications relay against the Jem'Hadar.
AR-558 is the site of a Dominion communications relay captured by Starfleet in The Siege of AR-558. Of the 150 soldiers sent to hold it, only 43 survive when the Defiant arrives with supplies, and the planet is strewn with Houdini mines that drift in and out of subspace.
Sisko takes command of the garrison when the Jem'Hadar attack. The defenders hold the relay at heavy cost, and Nog loses a leg in the fighting before relief arrives aboard the USS Veracruz.