The current modern Jewish calendar can not be used to accurately date historical events before 350AD. Although the structure of the calendar was not different, a very important and little appreciated detail in how the calendar was synchronized with the seasons has been overlooked. In this presentation I show evidence from the writings of Josephus. It can very easily be shown that the exact dates that Josephus records can not be reconciled with the current modern calendar. But they easily reconcile with the calendar based on the ripeness of the winter barley that was operating during Biblical times.