During what period was the calendar devised?
In what period did the calendar initially established?
In
which period did the timetable come into existence?
At what time was the timetable originally devised?
During what period was the timetable firstly conceived?
During what period did the timetable initially established?
In which period did the schedule generation?
In what period did the schedule emerge for the first time?
Keeping time The origin of BC and AD
