The preceding example of absolute dating begs the question: how do we actually know that Nero became emperor in 54 AD? In using the absolute chronology commonly used in historical scholarship and in large parts of the world, with the fixed point put at the supposed year of Christ’s birth, we tend to forget that both past and present know of several other absolute chronologies. Thus, before the 6th century AD, the specific Christian way of reckoning time did not yet exist. To convert the many different chronologies, absolute, but also relative, to one another is no easy task. One has to ask what, in a particular time reckoning, was the duration of whatever basic unit was employed, how this was subdivided, where the beginning of every unit or of longer cycles was located, and how units were named or numbered. Some examples might illustrate the remarkable complexity of this problem.
In ancient Egypt, a year was 12 months of 30 days each, with five festival days added. This year of 365 days gets out of pace with the sun, but the Egyptians did not use leap years. The years were counted from the succession of the reigning monarch. In Mesopotamia, many local calendars were in use, with different solutions to keep lunar months and solar years in track. The Assyrians named every year after the magistrates who oversaw the time reckoning (they are called eponymous magistrates, “magistrates who give their name”). The Babylonians originally numbered the years in a single sequence, but later they gave every year an individual name derived from some particular occasions. From the 16th century BC, we find regnal years in common use in Mesopotamia. Greece originally did not count years, but generations of variable duration; or the regnal years of the Persian monarch were referred to. In the 5th century, the tradition of naming of years after eponymous magistrates or monarchs established itself, and happily we have some lists of names that enable us to at least date texts or occurrences relatively. In Rome, the annual consuls were the eponymous magistrates, and later the regnal years of the emperors were used.
We also find systems comparable to the Christian chronology, using a fixed point: the so-called eras. To reckon time effectively in any such system, one needs a regular year, with leap years to stay in sync with the sun. Hellenistic rulers copied this from the Babylonians as the basis of their eras. Later, in 46 BC, Julius Caesar reformed the Roman calendar; this so-called Julian calendar was an improved version of the Egyptian solar calendar, with one leap day inserted every four years. An important era was the Seleucid era, with its fixed point in, to put it in our terms, 312 BC, which was widely used in the Near East, until well into the middle ages, and by the Syriac Church even to the present day. But in Hellenistic and Roman times, there were several other eras in use in monarchies and in individual cities. Roman historians reckoned from the founding of the city of Rome, in 753 BC. The Greeks had a time-honored era: the Olympiads. The Olympics were a festival in Olympia that was held every fourth year and which was important enough to serve as the basis for a Panhellenic chronology. The Olympics run from 776 BC in our terms (776 BC is Ol. 1.1, that is. the first year of the first Olympiad). Already in ancient Greece, the Olympiads were synchronized with lists of rulers and eponymics.
The Christian chronology was created in the 6th century. The monk Dionysius computed the future dates of Easter, which were based on the Jewish lunar calendar, but had to be fitted in with the Julian solar calendar. In the 6th century, the Diocletian era, which began with the first year of the reign of the emperor Diocletian, 284 AD, was still in common use, but Dionysius did not want to head his Easter table with a reference to a heathen emperor who persecuted the Christians. Instead, he computed the date of Christ’s birth and re-baptized the year 248 of the Diocletian era as the year 532 “after the incarnation of Our Lord.” Thus, a Christian era was born, adopted in the Byzantine Empire in the 6th century, and in the 8th century all over Christian Europe. Now dates expressed in the Diocletian era or in Olympiads could be converted into dates before or after Christ’s birth, the last year before Christ (1 BC) being immediately followed by the first year after Christ (1 AD).
In order to check whether our conversions of other dates into the Christian chronology are correct, we need information on events that are astronomically absolute and can be expressed unambiguously in the Christian chronology. Thus, an eclipse mentioned by an 8th-century Assyrian governor must have taken place on the 10th of June, 763 BC, and another eclipse reported by the Greek historian Thucydides can be dated to the 3rd of August, 431 BC. And so on and so forth. Now we are left with some certain dates. However, this does not mean that all our problems have been solved: the struggle to reconcile different methods of reckoning time, which began in antiquity, is still under way.
World History
