Why did they change original first month March to January?

The change of the first month from March to January dates back to the Julian calendar reform initiated by Julius Caesar in 45 BCE. Originally, the Roman calendar began in March, which aligned with the spring equinox and agricultural cycles. However, to better align the calendar with the solar year and to celebrate January, named after the god Janus, as a time of new beginnings, January was designated as the first month. This adjustment helped standardize the calendar and simplified administrative and civic planning.