Excalibur
One of the movie's taglines is "Before King Arthur, there was Excalibur". The last shots of the film establish the sword of Caesar as the legendary blade (also the Sword in the Stone, originally a different weapon).
The word Excalibur comes from the Old French Escalibor which is itself a corruption of Caliburnus or Caliburn. The name Caliburn is often held to be Geoffrey of Monmouth's Latinized form of the original Welsh Caledfwlch, which combines the elements caled ("battle, hard"), and bwlch ("breach, gap, notch"). Manfredi espouses an alternative theory wherein Caliburn derives from Latin chalybs "steel", which is in turn derived from Chalybes, the name of an Anatolian ironworking tribe.
The sword bears the inscription CAI • IVL • CAES • ENSIS CALIBVRNVS. The characters "CAI. IVL. CAES." are an abbreviated form of Caius (or Gaius) Julius Caesar. Manfredi loosely translates ensis caliburnus as "sword of steel". Ensis is one of the Latin words for "sword". While in reality Geoffrey of Monmouth's Latinization Caliburn eventually developed into the form Excalibur, the film explains the origin of the name Excalibur by having the inscription obscured by moss; the remaining letters spell out E S CALIBVR.
Read more about this topic: The Last Legion, Connections To Arthurian Legend