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The Romans had an interesting calendar. The lengths of their months were fixed and they had a 13th "intercalary" month that got inserted every few years to kee

The Romans had an interesting calendar. The lengths of their months were fixed and they had a 13th "intercalary" month that got inserted every few years to keep the months roughly in line with the seasons. Because everything was completely regular, everything was the same one year to the next, so you didn't need a unique calendar for each year. Consequently, calendars would be engraved in stone on public monuments and the wealthy would have a calendar painted onto a wall in their home. The year would be written out as a set of 13 columns, with each column being a month. They would then have the list of days in the month going down, and would note any holidays for the day. The only wrinkle in the Roman calendar were the "nundinae," which were (very loosely) a sort of Roman weekend. But the nundinae happened on an eight day cycle, so they didn't line up from one year to the next. The way they handled this was that they labeled each day in the year sequentially with a letter from A-H. Then all you needed to know was which letter corresponded to the nundinae for that particular year. (And, of course, whether that year had the extra 13th month.) Here's what a typical Roman calendar looked like: https://en.wikipedia.org/wiki/File:Museo_del_Teatro_Romano_de_Caesaraugusta.43.jpg https://en.wikipedia.org/wiki/File:Museo_del_Teatro_Romano_d...

oh_sigh 4y ago
How about: 13 months, each is always 28 days/4 weeks. At the end of the year there is a public holiday. Every leap year the public holiday is 2 days long. The hard part will be thinking of the name for the 13th month.
TedDoesntTalk 4y ago
> The lengths of their months were fixed and they had a 13th "intercalary" month that got inserted every few years to keep the months roughly in line with the seasons. This is precisely how the current Hebrew calendar works.
- antognini 4y ago
  Yes, pretty much every civilization that used a lunar calendar relied on an intercalary month getting added to keep the calendar in sync with the seasons. What made the Roman calendar unique was that it did not tie the months to the lunar phases. In the Hebrew and Babylonian calendars the month started on the first day that the lunar crescent was visible after a new moon. Since the synodic period of the Moon is about 29 and a half days this meant that the length of the month varied. In fact, much of the early development of Babylonian astronomy was likely motivated by the need to predict in advance how long a month was going to be (and whether a 13th month was going to be necessary). But because the Romans didn't care what the phase of the Moon was (at least by the middle Republic), they could fix the lengths of the months to be same every year.
deleted 4y ago
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oh_sigh 4y ago

How about: 13 months, each is always 28 days/4 weeks. At the end of the year there is a public holiday. Every leap year the public holiday is 2 days long. The hard part will be thinking of the name for the 13th month.

TedDoesntTalk 4y ago

> The lengths of their months were fixed and they had a 13th "intercalary" month that got inserted every few years to keep the months roughly in line with the seasons. This is precisely how the current Hebrew calendar works.

antognini 4y ago
Yes, pretty much every civilization that used a lunar calendar relied on an intercalary month getting added to keep the calendar in sync with the seasons. What made the Roman calendar unique was that it did not tie the months to the lunar phases. In the Hebrew and Babylonian calendars the month started on the first day that the lunar crescent was visible after a new moon. Since the synodic period of the Moon is about 29 and a half days this meant that the length of the month varied. In fact, much of the early development of Babylonian astronomy was likely motivated by the need to predict in advance how long a month was going to be (and whether a 13th month was going to be necessary). But because the Romans didn't care what the phase of the Moon was (at least by the middle Republic), they could fix the lengths of the months to be same every year.

deleted 4y ago

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