In the first #Roman #calendar, the year began on the day of the #moon's #FirstVisibleCrescent after the northward #equinox (which in #Rome is the spring equinox). Since the Romans thought #EvenNumbers were unlucky, #months could have 29 or 31 days, but there were only 10 months in the year; after Decembris, there was a long period outside any #month that the Romans just thought of as "like, #winter, I guess?"