How the Romans Changed the Months in the Calendar Year

The romans began each season with the vernal equinox. But they were using moon cycles to determine when the months changed, not the equinox or solstice. They weren't making regular adjustments to account for this discrepancy. The last month of february was used for adding days to resolve the discrepancies. It's also why we still use it to day, for adding the leap year every four years.