So the background is that I am working on some code to translate a Gregorian date to an Ancient Rome date. Upon Googling ancient roman dates I have the formula down pretty solid. However, I keep seeing different endings for months and special days (Kalends, Nones, Ides).

What is the correct set of rules for me to correctly determine the spelling of these days and months?

(ante diem|pridie) (lower case roman numeral?) (special day) (month) (year) (suffix [AD|AUC])

Just for an example, I've seen Kalends, Kalendas, Kalendis.. I've also seen Ianuarius, Ianuariis, etc.

I found this source: http://www.latin.org/datecalculator.php

Not sure if it is always correct...

  • 2
    I think this could be a better fit for the latin language stack(yes, there is one even for latin).
    – SJuan76
    Apr 21, 2017 at 20:43
  • Seconding @SJuan76.
    – user12566
    Apr 22, 2017 at 1:54
  • If you just want to write a date on or after 15 October 1582 in Latin, using the same wording as in ancient Rome, all well and good. But Gregorian dates are seldom used before that calendar was first instituted on 15 October 1582, and before about AD 9, it's impossible to convert exactly between modern or medieval calendars and the calendar as it was observed in Rome due to sketchy records. Apr 22, 2017 at 13:34

1 Answer 1


As per the comments, I went to Latin stack exchange and found my answer. I'll post here for googling purposes.


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