The
Roman new year's day (until year 153), and the day in which the
Consuls entered their office. The fact that March used to be the first month of the year can still be seen in the names of later months, for example:
September (septem=7),
October (octo=8),
November (novem=9) and
December (decem=10)
The day was a holiday for the god Mars.
It's also my birthday.