It is the best preserved sword of its type in the UK.
The blade and its scabbard mounts have been bought at auction by the Leeds-based national museum of arms and armour, and they are about to go on display alongside a replica of how the sword may have looked when carried by a Roman infantryman in the first century AD.
The fascinating weapon, an important sword of the Pompeii type, is decorated with engraved figures – possibly Mars, the Roman god of war, and Victory – and has a dot-punched inscription of the owner's name, Caius Valerius Primus.
The sword was discovered on a spoil heap in Germany in the early 1970s by an amateur archaeologist.
It was restored and preserved by its previous Swiss owner, Axel Guttmann, and formed part of his collection.
Royal Armouries director Peter Armstrong said the sword was a major acquisition for the museum and for the country as a whole.
"Even though the Roman Empire wielded power and influence for centuries, Roman swords are surprisingly rare and seldom become available to purchase," he said.
"The quality, type and provenance of this sword make it important in the UK.
"The Roman Empire is one of the most popular and fascinating periods in history, especially for children."
He added: "This sword dates from around the same time as the conquest of Britain and, whilst we already build events and interpretations around aspects of Roman life like gladiators and chariot racing, having this sword on display will enable us to bring the epic story of the Roman Empire even closer."
The sword will initially be exhibited in the Recent Acquisitions display at the Royal Armouries before being moved to the War Gallery where it will become a major object in the "Early War" section.

the word on the sword...
l It has a gladius blade of Pompeii type (so called after four examples found at Pompeii), and scabbard mounts.
l The parallel double-edged blade of piled construction is of flattened diamond section with reinforced tip and long tang. The blade is pointed for the last 76mm and the tip is reinforced for the last 31mm.
l The scabbard mounts comprising locket, appliqui palmette, chape (and modern collar) are of bronze with the remains of tinning, with cut-away and engraved motifs.
l The sheath itself, originally a wood body covered in leather has long since perished. The locket has two pierced and engraved panels decorated with two helmeted figures.
l The upper panel shows a warrior - possibly the god Mars - moving towards the right, his head turned back, holding spear and shield and wearing a muscled cuirass and crested helmet.