The months of January and also February were not originally in the ancient Roman calendar as the winter months were considered dormant, both in terms of agriculture but also in terms of making war. This was a time of peace. Until 450 BCE, the Roman calendar was 10 months, beginning in March (Martius), due to the March Equinox. Remember March was named for “Mars,” the god of War who was also an agricultural guardian. (source: https://www.almanac.com/content/month-january-holidays-facts-folklore)