In which period did the calendar devised?
When was the calendar initially introduced?
At what time did the calendar come into existence?
During what period was the schedule initially devised?
During what period was the agenda firstly envisioned?
When did the schedule firstly devised?
At what time did the agenda generation?
In which period did the calendar arise for the first time?
Mesoamerican Calendars and Archaeoastronomy