The Roman calendar originally didn’t last all year round. It began in the spring and ended at the start of winter, and then the winter period just didn’t exist on the calendar.
Calendars were invented to plan the growing of crops, so tracking the days in winter didn’t have any purpose, so they left winter out.
That’s also why the months are numbered wrong. If you know Latin, or at least one of the romance languages that derived from Latin, then "Septem"ber should be the 7th month, "Octo"ber should be the 8th month, "Novem"ber should be the ninth month, and "Decem"ber should be the 10th month. But that’s not how it works today, as we no longer count March as the first month of the year.
The Roman calendar originally didn’t last all year round. It began in the spring and ended at the start of winter, and then the winter period just didn’t exist on the calendar.
Calendars were invented to plan the growing of crops, so tracking the days in winter didn’t have any purpose, so they left winter out.
That’s also why the months are numbered wrong. If you know Latin, or at least one of the romance languages that derived from Latin, then "Septem"ber should be the 7th month, "Octo"ber should be the 8th month, "Novem"ber should be the ninth month, and "Decem"ber should be the 10th month. But that’s not how it works today, as we no longer count March as the first month of the year.