Gladius

The Gladius is the basic sword used by the Roman military as basic equipment for the Roman Legionair - and therefore most likely added to the basic armorment of a Roman Halfblood.

Other weapons given to Roman Legionairs are the shield, javelines, a dagger, and maybe some darts as well.

At the end of The Lost Hero Juno presented Jason with a Gladius to replace his lost weapon Ivlivs.