The oldest calendar **ever discovered** is a Mesolithic monument created by hunter-gatherer societies and dating back to around 8,000 BC, originally excavated in Aberdeenshire, Scotland, by the National Trust for Scotland in 2004. It pre-dates the first formal time-measuring devices known to Man, found in Mesopotamia, by nearly 5,000 years. (Source: University of Birmingham, published July 15, 2013, in the journal _Internet Archaeology_).

The oldest calendar **still in use** is the Jewish calendar, which has been in popular use since the 9th century BC. It is based on biblical calculations that place the creation at 3761 BC. (Source: _Guinness Book of World Records_).
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