Tracing the origins of the Mayan Calendar, I discovered that European medieval paintings, Greek vessels, rock art and texts such as the Bible and the Torah, contain mathematical codes hidden in designs and stories. The astronomical mathematical mechanisms that allow us to decipher, the hidden at plain sight messages, are the Mayan and the Aztec calendar.Recognizing that all ancestral religions shared the same knowledge, deprives us of arguments to discuss, and invites us to dialogue.The oldest rock art in the world suggests that the Neanderthals also used this calendar, and that the intellectual challenge that gave us humanity, was our astonishment at the movement of the stars.