Although this is mostly a life in the Middle Ages blog, with the Olympics getting started very soon, it seemed a good time to discuss their ancient origins.
The modern Olympic games (founded 1894) were inspired by the Olympian games of ancient Greece, hence the name "Olympic." But other than a general inspiration of having people from different states compete in athletic contests, they're really very different. And there was a millennium and a half gap between the end of the original Olympian games (or their Roman successors) and modern Olympics.
The original Olympian games were created as a ceremony to honor the Olympian gods (the 12 big ones you normally hear about, Zeus, Hera, Apollo, Artemis, and so on, but especially Zeus). We don't usually think of sporting events as religious ceremony, but the ancient Greeks did. Any sort of contest could be done in the gods' honor. Athens, for example, had annual play-writing contests in honor of the god Dionysus.
Starting in the eighth century BC (the traditional date is 776 BC), Olympian games were held every four years. Wars would stop for the duration of the games. The various city states into which Greece was divided would all compete, for the glory of their city. There were no medals, only an olive leaf wreath for the winner, and no second or third places. You either won by coming in first or else you lost. In spite of all their differences (and wars), Greek cities were united by coming together for the games.
The events were primarily of activities that would be useful in war, things like running, jumping, throwing spears, throwing the discus (which could be a deadly weapon), wrestling, and chariot racing. There was even a race run wearing armor. Women did not normally compete, although there was sometimes a foot race for girls.
The competitors were all amateurs in the sense that modern sports have forgotten--they spent most of their life doing ordinary things, not full-time athletic training. If they won, however, they would be richly rewarded by their city.
Competition was in the nude for most events. (Have you ever wondered why you never see Greco-Roman wrestling on TV? just joking!) There were several explanations for the nudity. A common story was that the men originally competed in breeches, until one time one's waistband snapped. He then either ran faster nude and won, or else got tangled up, fell to the ground, hit his head, and died, depending on which version you believed. The more likely explanation is that the Greeks weren't all that big on clothing anyway and considered a manly body worth putting on display.
The Romans took over much of Greek culture when they conquered the eastern end of the Mediterranean, and they originally continued the games. They introduced a number of events for women, though these seem to have been more a chance for the spectators to enjoy the sight of flashing legs (the women competed in short tunics) than genuine athletic contests.
The emperor Theodosius eventually ended the games in 393 AD, as part of a campaign to make Christianity the Roman state religion and end all old pagan ceremonies. But when the modern Olympics were created, the modern Greeks were eager to claim them as their heritage. Greece ("Hellas" as they themselves call their country) has its athletes march in first.
And they make sure that the former Yugoslav republic of Macedonia is called "the former Yugoslav republic of Macedonia," not just "Macedonia." For the Greeks, the name Macedonia evokes the northern part of Greece (bordering the former Yugoslav republic), where Alexander the Great came from, and they don't want "some Slavs" (as they would think of them) bearing a national name that to them is emphatically Greek.
In the US, we lose track of history before WW II, or even the Vietnam War. The rest of the world has much longer memories.