There is speculation that prior to the republic Roman calendar there was an earlier calendar instated by Romulus and consisting of ten months. I do not want to discuss here whether Romulus existed and whether, if he did exist, set up the calendar. I want to understand whether the calendar itself existed.
Over the years, I have seen sources claiming it as a fact that there was a pre-republican calendar from March to December and other sources claiming that there is no real evidence in its support. So, what written evidence is there in support of the alleged existence of a ten-month calendar starting in March? The text can be fragmentary old calendars, mentions in other literature, or something else. I would like to exclude the numbering of the names of the months Quintilis through December as indirect evidence and focus on remains or mentions of actual calendars.