This is a leather scabbard for the famous spartan swords featured in the epic Zack Snyder movie '300'.
The scabbard features hand-sewed real leather with real metal rivets and is marked "Stelios DBL" on the belt, probably meaning it was a doubled piece for Stelios hero sword scabbard or used by Michael Fassbender's stunt double on fight scenes, hence, screen used.
COA: Hollywood History
Image 2: Michael Fassbender as Stelios in a moment of the film where this scabbard can be seen clearly.