Intro page | How to Read the Tables | The Olympiad System | Sources | Analysis
These pages give access to conversion tables in Excel format, with copies in HTML format and in CSV format, useful for determining the Julian equivalent of years dated according to Olympiads during the Ptolemaic era. This system was used by Greek historians to provide a common frame of reference to reconcile historical dates given in many different local calendars. It is particularly important for interpreting the regnal years attributed to the Ptolemies by Porphyry, as transmitted through the works of Eusebius.
The Olympiad system is not a calendar in the normal sense. There is no unique method of counting days or months, only for counting years. Even the first year in each Olympiad only has a nominal starting point. In practice they can only be considered as running roughly from mid-summer to mid-summer unless we have other information about the source calendar of a particular set of information.
The system was based on a count of Olympic Games, which were held every four years. The four years between successive games constituted an Olympiad. Thus, according to the Olympic system, years were numbered by Olympiad and by the number of incomplete years since the last games: The first Olympic games were believed to have been held in summer of 776 BC, so:
Ol. 1.1 = 776/5
Ol. 1.2 = 775/4
Ol. 1.3 = 774/3
Ol. 1.4 = 773/2
Ol. 2.1 = 772/1 etc.
The exact date on which the Games and the festival were held, the nominal starting point of an Olympiad, is uncertain. The standard modern view is that the Olympic month was between the first and second full moon following the summer solstice, with the Olympic festival being held on the second full moon and the Games themselves having been held in the previous few days: see S. G. Miller, MDAIA 90 (1975) 215. The nominal dates included in the table here are calculated on this basis.
However, for chronological purposes, this issue is a minor detail. The system was established by Greek historians in order to provide a common framework, known and acceptable to all Greeks, for coordinating chronological data. Greek cities, and the non-Greek states who came into contact with the Greek world, each operated their own calendars independently of each other. These calendars each had their own month names, started at different times of the year, and, if Athens is a typical example, the months of Greek states were only loosely aligned to the moon, with days being repeated or omitted at will. Greek years were usually accounted eponymously, with the eponyms varying from city to city (archons in Athens, ephors in Sparta etc). Before the Olympic system came into use, Greek historians could only date events by cross-referencing several local systems; a well-known example is Thucidydes 2.2.1.
The Olympiad system allowed each of these eponym lists to be mapped to a single common system without maintaining a concordance of eponym lists for all the local cities involved. The first step was to establish a canonical sequence of Olympic victors -- i.e. an Olympic eponym list. According to Plutarch, Numa 1.4, this was undertaken by Hippias of Elis, who lived in the fifth century. A list of victors in the stadion events up to Ol. 249.1 = AD 217/8, believed to be taken from the work of Phlegon of Tralles, is preserved in Eusebius (ed. Schoene) Chronicorum I 193. The final form of the system, in which the Olympics and the individual years between them were numbered, was established by Eratosthenes of Cyrene in the third century. Eratosthenes' chronicle is almost entirely lost, but its authoritative status is clearly demonstrated by Dionysius 1.74.2, who discusses its central status to establishing Roman chronology.
The Olympic chronography which survived antiquity essentially intact is that of Eusebius, as transcribed in Jerome's Chronicon; the section relevant to the Ptolemies is available here. Eusebius was concerned with reconciling the events of biblical history with classical historical material. Since much biblical history predated the Olympic Games, Eusebius invented a new era, the Era of Abraham, but fortunately he also developed an approach to representing a compact concordance of many dating systems simultaneously, which allowed him to preserve the source dating systems. These include the Olympiads.
For a chronologist seeking to establish precision, an obvious disadvantage of the system is that the calendar years of the individual calendars mapped to the Olympic years were not synchronised to the Olympic year any more than they were synchronised to each other. To take only the calendars considered in these pages that were mapped to Olympic years, the Athenian year nominally started on the first new moon after the summer solstice, two or six weeks before the Olympics; the Roman consular year typically started in early spring; the Seleucid year typically started with the new moon following the autumnal equinox; the Egyptian year started on a solar date that slipped from mid November to late August; and the Egyptian Macedonian year moved from mid June to alignment with the Egyptian civil year.
Clearly, if the Olympic year were strictly aligned to the lunisolar anniversary of the Games, and the local calendar year started earlier or later, events near the beginning (or end, as appropriate) of the local year could easily be mapped to the wrong Olympic year. By transference, it was even easier to create false equations between the years of the individual systems that were mapped to a common Olympic year. This problem was recognised early on: Polybius 12.11 notes that the fourth-century historian Timaeus, who is the first historian known to have used Olympic dates (or at least Olympic eponyms) as a synchronistic tool, complained that the variance covered by the mapping of Olympic years to archon years in Athens, to ephor years in Sparta and to years of the Argolid priestesses of Hera amounted to three months. However, its advantages as a common yardstick clearly outweighed its inherent imprecision. Indeed, Polybius organised his own history around the system.
For modern chronologists, a second disadvantage of the system lies in the feature that was its greatest attraction to classical chronographers. As a result of its ability to act as a reference frame, the classical authors were able to discard the precise source dates that went into the concordance. The task of reconstructing the eponym lists for the various cities is a major problem, and for many we can make little progress. Moreover, unless we can identify the source calendar, we are often unable to improve on the precision of the Olympic data, and cannot detect problems of overlap. In short, we are often at the mercy of the accuracy of the classical chronographers, and the errors in the MS tradition that has transmitted their results to us. Careful comparison against all available sources, and against contemporary data, is needed to verify and improve upon them.
Finally, it should be stressed that Olympic dating was only ever used for historical purposes. Given its inherent imprecision, it was completely inappropriate for everyday life. As a result, we often do not know where critical events actually stood in relation to the Olympic Games. An oustanding example is the assassination of Philip II of Macedon, which happened in an Olympic year and almost certainly occurred within a very few weeks of the Games. Yet we have no idea whether he was assassinated before or after the Games.
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