The idea for that costume started after the developers learned about the God of War fans known as the Spartan Army. Thinking it would be cool to do a costume that would go with the Arms of Sparta and form a cohesive set of gear, they designed the Legionnaire Costume.
The helmet design was loosely based on that of a Spartan Soldier and the chest plate had elements like the Cerberus silhouettes found on Kratos' Armor from the God of War flashbacks. The developers also wanted to carry the crimson elements of Kratos’ tattoo and cloth skirt into that costume in order to keep his palette familiar.
That costume granted Kratos the ability to collect double Orbs of all types and using magic cost half the amount of Blue Orbs. On top of that, the Legionnaire resisted enemy damage four times as much as normal and dealt double damage with the Arms of Sparta. If playing a bonus game using both this costume and The King's Ring, the player will obtain 20 times more red orbs than usual.
The Legionnaire Costume was unlocked through a code that was obtained by pre-ordering the game.
God of War: Origins Collection
All the previously pre-order exclusive content (including that costume) was included with the game.