From what I have heard/read (I wasn't around at the time, so this is all hearsay, obviously) - both the Egyptians and the Mesoamerican people knew the correct year length (the Mesoamerican even at least as precise as our 365.24219 days) - not due to precise instruments, but through patient long-term observation. But they refrained from modifying anything in their calendar, for fear of invoking the wrath of some god or another - well, one Pharao tried, but his priests didn't follow.

Much later (but earlier than any pope), the romans had a god named Terminus, who was the god of border stones and limits (yes, the word "terminal" is derived from his name, an airport terminal is at the boundary between "on the ground" and "up in the air", and someone terminally ill is at a boundary, too). The romans didn't even dare to move an altar dedicated to him (or maybe it was a mere border stone, as all border stones were kind of an altar for Terminus), at a place where a Zeus temple was about to be constructed, instead they left a hole in the roof of Zeus' temple, to fulfil the condition that Terminus' altar remain under the open sky.

This god, as most others, had a festival, and his, of course, was under no circumstances to be moved, either. So, when the romans noticed that - with a fixed-number-of-days year length - the year would move through the seasons, they feared that might invoke the wrath of this god, and so they did opt to use leap days.

In order to maintain the correct distance between the day of Terminus' festival, and both the beginning and the end of the year, they inserted any correction days (at least once even a whole month) at that specific date, which is the reason why most popes observed their leap days on February 24 (with any festivities between Feb.24 and Feb.28 in leap years moved by a day). Not before 1969 did the Pope have his leap day on February 29.

I believe that's mostly baloney, starting with the assertion that the concept of terminal derives from the name of the god, whereas in fact it was the other way around.

In any case, you've left out what I feel is a more important fact: that the ancient Roman calendar began with March. This is why February is the month with the oddball (and varying) number of days. (It is also why the names of the months of September, etc. make (or made) sense.)

I refer all interested to this wikipedia article.

I reckon we are the only monastery ever to have a dungeon staffed with 16,000 zombies.

I thought the months started with January, because that month was named after the two-faced Roman god Janus, god of beginnings/endings and doors. (Janitor comes from Janus, for example.) There were ten months, finishing with December, the tenth month (the year's last four months are September, October, November, December -- months 7, 8, 9, and 10). Then Julius Caesar added two months in the summer, named after himself (Julius Augustus Caesar, hence July and August) to get to twelve months.

Alex / talexb / Toronto

Thanks PJ. We owe you so much. Groklaw -- RIP -- 2003 to 2013.

whereas in fact it was the other way around

Yes, that was my novelist alter ego going overboard with me ;-)

But I stick to the theory that it were the Romans and their high priests who made leap years popular (see this other Wikipedia article). And i stick to the leap day being February 24.

How could I forget the year started in March! Yes, I had read that, too, and it coincides with the fact that my favourite algorithm (from 1963) (partially explained here) (in ALGOL) starts out with

if m > 2 then
   m := m - 3
else begin
   m := m + 9
   y := y - 1
end
[download]

thus re-scaling the year from 1=January .. 12=December to 0=March .. 11=February (only for easement of the calculation, not because of history, but that makes it even nicer)

use warnings;
use strict;

for(1900, 2000, 2100, 2200, 2300, 2400, 1964, 1965, 1966, 1967, 1968) 
+{
   print "$_\n" if is_leap_year($_);
}

sub is_leap_year {
  my $year = shift;
  return !($year % 400) || $year % 100 && !($year % 4);
# Or:
# return !($year % 400 && !($year % 100) || $year % 4);
}
[download]

Yeah, I got the code wrong.