As mentioned above, Rome's legendary 10-month calendar notionally lasted for 304days but was usually thought to make up the rest of the solar year during an unorganized winter period. The unattested but almost certain lunar year and the pre-Julian civil year were long, with the difference from the solar year more or less corrected by an irregular intercalary month. The Julian year was 365days long, with a leap day doubled in length every fourth year, almost equivalent to the present Gregorian system.