thumb | 300px |Stadium at ancient [[Olympia, Greece|Olympia]]
An olympiad (, Olympiás) is a period of four years, particularly those associated with the ancient and modern Olympic Games.
Although the ancient Olympics were established during Greece's Archaic Era, it was not until Hippias that a consistent list was established and not until Ephorus in the Hellenistic period that the first recorded Olympic contest was used as a calendar epoch. Ancient authors agreed that other Olympics had been held before the race won by Coroebus but disagreed on how many; the convention was established to place Coroebus's victory at a time equivalent to the summer of 776BC in the Proleptic Julian calendar, and to treat it as Year 1 of Olympiad 1. Olympiad 2 began with the next games in the summer of 772BC.
Thus, for N less than 195, Olympiad N is reckoned as having started in the year <math>780-(4\times N)</math>BC and ended four years later. For N greater than or equal to 195, Olympiad N began in AD<math>(4\times N)-779</math> and ended four years later. By extrapolation, the year of the st Olympiad begins roughly around 2 August .
In reference to the modern Olympics, their Olympiads are four year periods beginning on 1 January of the year of the Summer Games. Thus, the I Olympiad began on 1 January 1896, the II Olympiad began 1 January 1900, and so on. The XXXIII Olympiad began 1 January 2024. Because the Julian and Gregorian calendars go directly from 1BC to AD1, the cycle of modern Olympiads is ahead of the ancient cycle by one year.
Ancient Olympics
Each olympiad started with the holding of the games, which originally began on the first or second full moon after the summer solstice. After the introduction of the Metonic cycle about 432 BC, the start of the games was determined slightly differently. Within each olympiad, time was reckoned by referring to its 1st, 2nd, 3rd, or 4th year. Ancient writers sometimes describe their Olympiads as lasting five years but do so by counting inclusively; in fact each comprised a four year period. For example, the first year of Olympiad 140 began in the summer of 220BC and lasted until the middle of 219BC. After the 2nd, 3rd, and 4th years of Olympiad 140, the games in the summer of 216BC would begin the first year of Olympiad 141.
Historians
The sophist Hippias was the first writer to compile a comprehensive list of the Olympic victors (, olympioníkes). Although his Olympic Record (, Olympionikō̂n Anagraphḗ) is now entirely lost, it apparently formed the basis of all later Olympic dating. The numbering of Olympiads was introduced by Eratosthenes or Timaeus; the first on the list occurred in 776 BC. The panhellenic nature of the games, their regular schedule, and the improved victor list allowed Greek historians from Eratosthenes onwards to use the Olympiads as a way of reckoning time that did not depend on the various calendars of the city-states. The first to do so consistently was Timaeus of Tauromenium in the third centuryBC. Nevertheless, since for events of the early history of the games the reckoning was used in retrospect, some of the dates given by later historian for events before the 5th centuryBC are very unreliable. Because the Olympics occurred in mid-summer, the years reckoned by the Olympiad system aligned with the Attic calendar (which names years by the names of archons, not numbers) of Ancient Athens, but not with Roman consular years (which began on 1 January) or Ancient Macedonian calendar years (which began in the autumn).
In the 2nd century, Phlegon of Tralles summarized the events of each Olympiad in a book called Olympiads; fragments survive in the work of the Byzantine writer Photius. Christian chroniclers continued to use this Greek system of dating as a way of synchronizing biblical events with Greek and Roman history. In the 3rd century, Sextus Julius Africanus compiled a list of Olympic victors up to 217BC, and this list has been preserved in the Chronicle of Eusebius.
Examples of Ancient Olympiad dates
thumb|300px|A relief of the Greek Olympiad
- Early historians sometimes used the names of Olympic victors as a method of dating events to a specific year. For instance, Thucydides says in his account of the year 428 BC: "It was the Olympiad in which the Rhodian Dorieus gained his second victory."
- Dionysius of Halicarnassus dates the foundation of Rome to the first year of the seventh Olympiad, 752 & 751BC. Since Rome was founded on 21 April, which was in the last half of the ancient Olympic year, it would be 751BC specifically. In Book 1 chapter 75 Dionysius states: "...Romulus, the first ruler of the city, began his reign in the first year of the seventh Olympiad, when Charops at Athens was in the first year of his ten-year term as archon."
- Diodorus Siculus dates the Persian invasion of Greece to 480BC: "Calliades was archon in Athens, and the Romans made Spurius Cassius and Proculus Verginius Tricostus consuls, and the Eleians celebrated the Seventy-fifth Olympiad, that in which Astylus of Syracuse won the stadion. It was in this year that king Xerxes made his campaign against Greece."
- Jerome, in his Latin translation of the Chronicle of Eusebius, dates the birth of Jesus Christ to year 3 of Olympiad 194, the 42nd year of the reign of the emperor Augustus, which equates to the year 2BC.
Anolympiad
Though the games were held without interruption, on more than one occasion they were held by others than the Eleians. The Eleians declared such games Anolympiads (non-Olympics), but it is assumed the winners were nevertheless recorded.
End of the era
During the 3rd century, records of the games are so scanty that historians are not certain whether after 261 they were still held every four years. Some winners were recorded though, until the 293rd Olympiad of AD393.
Although the end of the games has sometimes been linked to the anti-pagan laws of Theodosius I (391–392) or Theodosius II (435), this is no longer widely accepted. The last games at Olympia were probably held in the first half of the 5th century. The last datable Olympic festival took place at Antioch in 520. Dating by Olympiads survived the Olympics themselves. The Chronicon Paschale dates events by Olympiad down to the 352nd Olympiad (AD628).
Modern Olympics
{| class = "wikitable sortable nowrap floatright"
! Olympiad !! First year !! Last year !! Host city !! Country
|-
| I (1st) || 1896 || 1899 || Athens || Greece
|-
| II (2nd) || 1900 || 1903 || Paris || France
|-
| III (3rd) || 1904 || 1907 || St. Louis || United States
|-
| IV (4th) || 1908 || 1911 || London || Great Britain
|-
| V (5th) || 1912 || 1915 || Stockholm || Sweden
|-
| VI (6th) || 1916 || 1919 || <s>Berlin</s> || <s> Germany</s>
|-
| VII (7th) || 1920 || 1923 || Antwerp || Belgium
|-
| VIII (8th) || 1924 || 1927 ||Paris || France
|-
| IX (9th) || 1928 || 1931 || Amsterdam || Netherlands
|-
| X (10th) || 1932 || 1935 || Los Angeles || United States
|-
| XI (11th) || 1936 || 1939 || Berlin || Germany
|-
| rowspan=2 | XII (12th) || rowspan=2 | 1940 || rowspan=2 | 1943 || <s>Tokyo</s> || <s> Japan</s>
|-
| <s>Helsinki</s> || <s> Finland</s>
|-
| XIII (13th) || 1944 || 1947 || <s>London</s> || <s> Great Britain</s>
|-
| XIV (14th) || 1948 || 1951 || London || Great Britain
|-
| XV (15th) || 1952 || 1955 || Helsinki || Finland
|-
| XVI (16th) || 1956 || 1959 || Melbourne || Australia
|-
| XVII (17th) || 1960 || 1963 || Rome || Italy
|-
| XVIII (18th) || 1964 || 1967 || Tokyo || Japan
|-
| XIX (19th) || 1968 || 1971 || Mexico City || Mexico
|-
| XX (20th) || 1972 || 1975 || Munich || West Germany
|-
| XXI (21st) || 1976 || 1979 || Montreal || Canada
|-
| XXII (22nd) || 1980 || 1983 || Moscow || Soviet Union
|-
| XXIII (23rd) || 1984 || 1987 || Los Angeles || United States
|-
| XXIV (24th) || 1988 || 1991 || Seoul || South Korea
|-
| XXV (25th) || 1992 || 1995 || Barcelona || Spain
|-
| XXVI (26th) || 1996 || 1999 || Atlanta || United States
|-
| XXVII (27th) || 2000 || 2003 || Sydney || Australia
|-
| XXVIII (28th) || 2004 || 2007 || Athens || Greece
|-
| XXIX (29th) || 2008 || 2011 || Beijing || China
|-
| XXX (30th) || 2012 || 2015 || London || Great Britain
|-
| XXXI (31st) || 2016 || 2019 || Rio de Janeiro || Brazil
|-
| XXXII (32nd)