Calendrical Conversion


An example of simple calendrical con­ver­sion can be seen in the cal­en­dar of the Maya. The Mayan cal­en­dar is a com­plex integ­ra­tion of cycles from 13 days, to twenty days, to the solar year to pro­duce a great cycle of fifty-two years (Aveni 1989: 185–252). The cal­en­dar fol­lows its own numer­ical logic but eth­no­graphic evid­ence allows us to recon­struct the work­ing of this cal­en­dar. We are there­fore able to con­vert the Mayan scale with its unique rela­tion­ship with the solar year and con­vert it into the mod­ern luni-solar cal­en­dar. The suc­cess of con­ver­sion is because Mayans were con­sid­er­ate enough to use a numer­ical cal­en­dar which is eas­ily inter­preted by mod­ern investigators.

Considerate is not a word fre­quently applied to the Romans, and their cal­en­dar poses more ser­i­ous prob­lems for archae­olo­gists. In the later, imper­ial, period the basis of the cal­en­dar were the reigns of the emper­ors. In the repub­lican period it was the names of the con­suls that gave the name to the year. Therefore to con­vert Roman dates, or any dates which rely upon the reigns of rulers, we must have access to an accur­ate his­tor­ical record to allow us to trace the dates.

Unfortunately the earli­est his­tory, that of Herodotus, dates only as far back as the late fifth cen­tury. Beyond this date there may be records of rulers, but they become more sus­cept­ible to his­tor­ical drift as date-keeping errors accu­mu­late. For this reason while we can trace the earli­est dyn­asty of Egypt back to the middle of the fourth mil­len­nium (Renfrew & Bahn 1996: 123), the error involved in doing so is con­sid­er­able, being around two cen­tur­ies. For pre­his­toric time, or arte­facts which can­not be dated his­tor­ic­ally we need a sys­tem of time-keeping inde­pend­ent of human action.

For other meth­ods of dat­ing see the con­tents page of the series Dating for Archaeologists.