The society, in recent decades, is characterized by growing immigration population, making it multicultural. New strategies are required for the smooth integration of the new citizens within their daily activities, including their education. Specifically, for the course of Mathematics, a new term examining the way the cultural background of a person is related with the way the person comprehends and uses Mathematics in daily basis, has been created by Ubiratan D’Ambrosio in 1987 and is called Ethnomathematics. There has been researching over the years on how ethnomathematical approaches could be inserted in class, for helping students increase their performance and reach higher grades in Mathematics. Our paper is intending to introduce ancient calendars as an ethnomathematical approach, by analyzing four ancient calendars: the Attic calendar, the calendar of Romulus, the calendar of Numa and the old Icelandic calendar misseri, introducing, moreover, a didactic proposal which may increase students’ interest for Mathematics and help them understand how each civilization used Mathematics for managing the time.