Page "Roman military diploma" Paragraph 5

Diplomas were not normally issued to discharged legionaries, as the legions recruited Roman citizens only.

However, legionary diplomas were exceptionally issued after the Civil War of 68 / 69 AD.

As an emergency measure, 2 new legions, the I and II Classica ( later reconstituted and renamed as I and II Adiutrix, respectively ) were formed mainly from naval marines, many of whom did not hold citizenship.

At the end of the crisis, these were all awarded Roman citizenship.