The olympic truce
In ancient Greece, a truce was held during the olympic games
During the olympic games of Olympia, as well as the today far lesser known Pythian games of Delphi, Nemeic games of Nemea and Isthmian games of Corinth, the Greeks did indeed keep a kind of truce, ekecheiria - but this truce did not imply that all wars between Greeks everywhere took a break, just that people who were going to participate in the games (as athletes, administrators or spectators) were to be left alone. Wars were allowed, as long as they didn't interrupt the games in any way. Splendid as it is, it's nowhere near the panhellenic celebration of peace one might have in mind.
Simon Hornblower makes an excellent description of the truce, consulting several good sources. The one I find particularly compelling is Thucydides; in his work on the peloponnesian war, during which several olympic games took place, a general olympic truce is never mentioned. Being a very careful author indeed, Thucydides couldn't possibly have overlooked such an event, by mistake or otherwise, in particular since he describes numerous other truces and armistices, of much lesser importance than the general idea of ekecheiria.
OK, on one single occasion it's mentioned; that's when the lakedaimonians of
Sparta in the olympic year of 420 BC attacked two villages in or near the city state
of Elis. That's where Olympia was, and the games thus occupied all citizens, which
were thus protected by the ekecheiria. According to Hornblower, the villages
were considered elean by the Eleans but not by the Lakedaimonians, thus making the
protected status a question of geography.
Hornblower also mentions his own favourite, Pindar, who specialized in writing songs for victorious athletes in the games (all four of them). The truce is all but left unmentioned; the single instance when it's there isn't even related to an olympic winner but an isthmian one, in which he mentions "the Elean truce-bearers of Kronos' son Zeus". This is another case of negative proof - the total, panhellenic truce would of course have been far more interesting to write about.
Hornblower pokes some fun at The International Olympic Truce Centre, an organization with goals that, however noble, are essentially based on a myth. There are of course quite a few people, within the IOC as well as outside, who honestly believe in the myth, and it's mentioned several times on their websites on the matter, but e.g. this definition is, upon closer examination, actually quite right:
Subsequently, all the other Greek cities ratified this "international agreement", thanks to which permanent, recognised immunity of the sanctuary of Olympia and the region of Elis became a reality. During the Truce period, the athletes, artists and their families, as well as ordinary pilgrims, could travel in total safety to participate in or attend the Olympic Games and return afterwards to their respective countries. As the opening of the Games approached, the sacred truce was proclaimed and announced by the Spondophoroi, citizens of Elis, who travelled throughout Greece to pass on the message. Proof that this Truce was respected is that, in Olympia, the Greeks never built walls to protect themselves, unlike all the other Greek cities.
IOC: The Olympic Truce
The first city walls of Olympia were erected about 260 AD, for protection against the non-hellenic heruls, so that part could be valid; but that Elis did not enjoy a permanent truce is proved by the events that Thucydides recorded, as well as several others. But the major problem with this definition is that, despite being written by someone who obviously knows that the truce was not such a major one as is generally assumed, it doesn't point that out, but instead describes it in a way which nobody who doesn't know the facts can't help but interprete as a confirmation of the general, nation-wide truce - which it isn't.
Olympos / Olympia
The olympic games were held in Olympia, not on Mount Olympos. There are actually several Mount Olympos in Greece, but the tallest (2917 m) and the one that's most likely the home of the gods is located in Thessalia, 250 km northwest of Athens. Olympia of the games is found on the west of the Peloponnes, 160 km southwest of Athens.
Regarding the Olympic games as a symbol of panhellenic unity, neither Herodotos nor Pindar writes of anything like that (nor any other greek author of the time) - "significant silence", as Hornblower puts it. There is a hint of a hint in the Lysistrata of Aristophanes in 411 BC, where "the common panhellenic altar" is mentioned, and in 380 BC a certain Isokrates wrote that "after concluding truces with each other and putting an end to any current hostilities, we come together in one place" - which, great as it sounds, was purely aspirational.
(Note: The image of the ancient Greeks as a democratic people of philosophy and wisdom, unlike e.g. the brutal Romans, has nothing to do with reality. The Greeks spent quite a lot of time on wars, the one chronicled by Thucydides being one among many. The image of the peaceful games is equally false; athletes occasionally died. The winners certainly didn't object to monetary rewards, though the decorations given at the games were purely symbolic, including the famous wreaths of laurel (other materials were used in the other games).
The olympic rings
This is not an ancient symbol of the games. The flag was first used in Alexandria in 1914 (not in an olympic year, that is), the rings being symbols of the five games that had been held up to that date, excluding the ones in Athens 1906. Since such a tradition would, in due time, yield a very complicated symbol indeed, it was soon changed. The rings now symbolize the five continents and nothing else.
The official definition does not, however, tell us which colour represents which continent. There are, of course, several such definitions, but that is another matter entirely. None is more correct than the other.
It includes the five interlaced rings, which represent the union of the five continents and the meeting of athletes from throughout the world at the Olympic Games.
From the Olympic Charter: the complete
The five continents usually mentioned are Europe, Asia, Africa, Oceania and America. Whether this is according to the original intensions is an open question; my personal guess is that Coubertin considered North America and South America two distinct continents, and never once thought about Oceania.
During the Berlin games in 1936 Leni Riefenstahl, the famous director of Triumph des Willens, directed the documentary Olympische Spiele, or Olympia in english. There's a scene in Delphi where a man carrying the torch runs past a stone with the famous five rings. The fact that such a stone is apparently still present at the stadion of Delphi has fooled quite a few people into believing the rings were used in ancient times, but the stone was made for the film.
The idea that the rings on the flag came from Delphi, and not the other way round, was
first brought forward by Lynn and Gray Poole in 1963, in History of Ancient Olympic
Games. Completely wrong as it is, it has still managed to survive, somehow. That's how
The olympic fire
Another ancient symbol
Some assume that the olympic fire was carried around by torch-bearers in ancient times. It wasn't; there probably was a fire present during the games, to symbolize the olympic truce (...) but the torch-running didn't show up in the modern games until Amsterdam 1928. The first time it was lit in Olympia in Greece to be carried to the arena? Berlin 1936.