<P> A number of prehistoric structures have been proposed as having had the purpose of timekeeping ( typically keeping track of the course of the solar year ) . This includes many megalithic structures , and reconstructed arrangements going back far into the Neolithic period . </P>
<P> A number of prehistoric structures have been proposed as having had the purpose of timekeeping ( typically keeping track of the course of the solar year ) . This includes many megalithic structures , and reconstructed arrangements going back far into the Neolithic period . </P>
when did humans start keeping track of years
when did humans start keeping track of years
going back far into the Neolithic period
going back far into the Neolithic period