<P> A mesolithic arrangement of twelve pits and an arc found in Warren Field, Aberdeenshire, Scotland, dated to roughly 10,000 years ago, has been described as a lunar calendar and dubbed the "world's oldest known calendar" in 2013 . </P> <P> The Oldest European calendar is found near to Vukovar in modern day Croatia . It is a ceramic vessel bearing inscribed ideograms of celestial objects </P> <P> The ancient Sumerian calendar divided a year into 12 lunar months of 29 or 30 days . Each month began with the sighting of a new moon . Sumerian months had no uniform name throughout Sumer because of the religious diversity . This resulted in scribes and scholars referring to them as "the first month", "the fifth month" etc . To keep the lunar year of 354 days in step with the solar year of 365.242 days an extra month was added periodically, much like a Gregorian leap year . There were no weeks in the Sumerian calendar . Holy days and time off from work were usually celebrated on the first, seventh and fifteenth of each month . In addition to these holy days, there were also feast days which varied from city to city . </P> <P> Although the earliest evidence of Iranian calendrical traditions is from the second millennium BCE, predating the appearance of the Iranian prophet Zoroaster, the first fully preserved calendar is that of the Achaemenids . 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 symbol in Iranian culture and is closely related to the folklore regarding Cyrus the Great . </P>

Where did the 12 month calendar come from
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