In principle, the position of #Mercedonius was supposed to switch back and forth in alternate #LeapYears, but this was never consistent. Even if it was, it would result in a mean year of 366.25 days, this giving a calendar that didn't track the #sun OR the #moon, because the #Romans were just *the worst* at timekeeping.

But wait! It gets worse!

#RomanCalendar

The extra month in the #RomanCalendar was called #Mercedonius, and it *nominally* fell in the 2nd and 5th years of a five-year cycle.

Some say Februarius was shortened and Mercedonius lasted 27 days, others that Mercedonius was 23 days long and the rest of Februarius came after the end of Mercedonius, but neither is really the case. As far as the #Romans were concerned, the kalends of Mercedonius came 11 or 11 days after the ides of Februarius and that was that.