<P> The course of the Sun and the Moon are the most evident forms of timekeeping, and the year and lunation were most commonly used in pre-modern societies worldwide as time units . Nevertheless, the Roman calendar contained very ancient remnants of a pre-Etruscan 10 - month solar year . The first recorded calendars date to the Bronze Age, dependent on the development of writing in the Ancient Near East, the Egyptian and Sumerian calendars . </P> <P> A large number of calendar systems which were based on the Babylonian calendar, and which were found in the Ancient Near East, date from the Iron Age . Amongst such calendar systems was the calendar system of the Persian Empire, which in turn gave rise to the Zoroastrian calendar as well as the Hebrew calendar . </P> <P> A great number of Hellenic calendars developed in Classical Greece, and with the Hellenistic period also influenced calendars outside of the immediate sphere of Greek influence, giving rise to the various Hindu calendars as well as to the ancient Roman calendar . </P> <P> Calendars in antiquity were lunisolar, depending on the introduction of intercalary months to align the solar and the lunar years . This was mostly based on observation, but there may have been early attempts to model the pattern of intercalation algorithmically, as evidenced in the fragmentary 2nd - century Coligny calendar . </P>

Are there any countries that don't use the gregorian calendar