Month names collection / metastudy

[DG97EEB]

Normally we see martius or martii, not martio. Same with seeing aprilis, ap'lis, april', not aprili. There is also an augusto in the text. 

magio is not normal latin as far as I am aware. We have maius, mai, mayus, may, maii, even madius.. and maggio is modern italian.

"Yes, martio can be ablative. Specifically, it is the singular masculine or neuter form of the Latin adjective mārtius ("of Mars" or "of March") in both the ablative and dative cases.
Because month names function as adjectives in Latin, you will most frequently encounter martio in time-related constructions. For example:
• Mense Martio: "In the month of March" (where martio is an ablative of time matching the ablative noun mense).
• Campus Martius: In the phrase in campo Martio ("on the Campus Martius" / "Field of Mars"), both words are declined into the ablative."

Just Google...