Basically I would like to know what the year "0" was for Romans ( if they even had such a concept) and why it was from that year. If there were other calendars for which you know this I would also be interested in them.
The Romans of the Roman Republic named their years based on their consuls (the two two chief administrators of the Republic, elected for one year). So the year that Cicero and Hibrida were consuls would be "The Year of M. Tullius Cicero and C. Antonius Hibrida". Occasionally they would date from the founding of the city (in 753 BC) but that was much less common.
Here are some threads on it: https://m.reddit.com/r/AskHistorians/comments/2gyy2d/how_were_dates_written_in_ancient_rome/
reddit.com/r/AskHistorians/comments/2pcmzb/what_was_the_startevent_of_the_roman_or_any_other/