The Creation of the Calendar Written by Pam Preedy. How old is timekeeping? Historians believe that timekeeping (and the calendar) goes as far back as the Neolithic period. Recent research suggested that Stonehenge (2,500BC) was originally built to track a solar year of 365.25 days. The Sumerians divided the year into 12 lunar months, each comprising 29 or 30 days, giving a total of 354 days. According to legend, Romulus, the founder of Rome, instituted the calendar in about 738 BC, though it is more likely to have evolved from…