The official calendar was a basic Roman institution, regulated by the pontiffs and governing the timing of all state business. Several calendars inscribed on stone or painted on walls have survived, recording month by month the dates of the major religious festivals and the days on which assemblies could meet and justice be administered (BNP 2.60–77). During the republic the official Roman year consisted of 354 or 355 days, necessitating intercalation (the periodic insertion of an additional month) to keep the calendar in synchronization with the seasonal calendar and the solar year. Intercalation was neglected during the political disturbances of the 50s BCE and the civil wars that followed. Julius Caesar, as pontifex maximus, introduced a solar calendar that is still in use today, known first as the Julian calendar and later, after slight modifications introduced in 1582 by Pope Gregory XIII, as the Gregorian calendar.