text: Ancient calendars The earliest evidence of Iranian calendrical traditions is from the second millennium BC and possibly even predates the appearance of the Iranian prophet Zoroaster. The first fully preserved calendar is that of the Achaemenids, a royal dynasty of the 5th century BC who gave rise to Zoroastrianism. Throughout recorded history, Persians have been keen on the idea and importance of having a calendar. They were among the first cultures to use a solar calendar and have long favoured a solar over lunar and lunisolar approaches. The sun has always been a religious and divine symbol in Iranian culture and is the origin of the folklore regarding Cyrus the Great.
  Old Persian calendar
  Old Persian inscriptions and tablets indicate that early Iranians used a 360-day calendar based on the solar observation directly and modified for their beliefs. Days were not named. The months had two or three divisions depending on the phase of the moon. Twelve months of 30 days were named for festivals or activities of the pastoral year. An intercalation month was added periodically to keep the calendar synchronized with the seasons.
  The following table lists the Old Persian months, alongside the approximate Gregorian months and approximate Babylonian lunar months.