There's a nice summary of ancient boxing showing up at a couple of Boxing sites ... here's the incipit of one from East Side Boxing:

Unarmed combat was most likely practiced by humans since before we were humans. In Western culture it is the Greeks who are first credited with taming the practice for sport. Known as “Pygmahia” or “fistfighting”, the ancient Greeks asserted that the sport was invented by Apollo, the sun god. In this tradition, the first mortal Champion Of The World was a prince named Forvanta. He represented mankind in the first recorded Championship; a match between man and god. Forvanta challenged Apollo and for this outrage Apollo killed the human Champion during their match.

Other victims of Apollos were Phorbas, a mortal boxer who challenged travellers wishing to pass through Delphi (he was also killed) and none other than the god of war Aries, who fell victim to the sun god at the mythic first Olympic games but lived to tell the tale. Other mythological practitioners of the sport included Herakles, Tydeus, Polydeusus and Theseus.

The first known boxing artifacts derive from ancient Crete, dating 1600 BC. The sport receives its first literary mention in Homer’s “The Iliad” (circa 800 BC), in the 23rd chapter, wherein Epeus (builder of the Trojan horse) and Euryalus (a Captain of the Argonauts) hold a contest at the funeral of Patroclus.

Patroclus was Achilles’ squire and had met his end in his master’s armour at the hands of Apollo and Hector during the Trojan War (1200 BC). The passage presents the sport of boxing as having already achieved a near modern sophistication - complete with rules and even seconds - and as with today’s version of the sport, the jaw is ever the target.

The Olympic games were reputed to have been founded by the gods, and were brought to this mortal coil by one Aethlius (from whose name is derived todays word “Athlete”) as a challenge to his sons. After a period wherein their practice was ceased, they were ‘revived’ by Iphitus and Lycurgus, two descendants of Herakles, in 766 BC as a means of replacing war with sport in the ancient world. These games featured only one event: The Stadion (chariot) race. Further events were added as the centuries passed. It wasn’t until 688 BC, at the 23rd Olympic games, that mankind first officially practiced the sport of boxing at an international level (as the Olympic games were open to all Greek-speaking males and one needed not be Greek by birth).

The ideal boxer at the time was aggressive and the bouts - fought naked save for hands wrapped in hard leather thongs called “cesti” - went until one of the two contenders signalled submission by raising his opened hand, or by taking a knee. An umpire was on-hand to ensure that the winner recognised this surrender. The first recorded Champion was Onomastos of Smyrna. He won the title in the 23rd games and thereafter set the rules for the sport, which were the first in recorded history.

Boxing did not take place in a ring, which meant there was no opportunity for cornering - rather, the Greeks placed portable barriers such as ladders or sticks on the ground to set the boundaries. These objects could be moved closer until fighters were forced to stand toe-to-toe. Because all fights were outdoors, a common tactic was to gain an advantage by standing so the sun was in an opponent's eyes.

There were no weight classes, no rounds and no time limit. Some fights lasted for days. If both fighters agreed, they could end the fight by “klimax’ whereby each fighter took turns striking the other, without pretense of defence by either, until a winner was decided. Athletes were selected by their city-states to represent their people, and although there were no weight classes it was obvious that size, height, weight, reach and strength were all advantages, therefore it was normally only the largest men who were chosen to represent their city-states in this sport.

The punching of the time was crude, and did not feature the straight punches normally seen today, but instead consisted mainly of wild hooks and hammer-like blows, mostly to the head. When defending, style and grace of movement were highly valued. Greek boxers trained for months before the games, because encounters between athletes armed with such terrible weapons as the cestus were bound to result in very serious injuries. In the days of Onomastos, courage was also valued and it was said that a fighter of the time named Eurydamas swallowed his own broken teeth rather than show that he was hurt. His opponent, disheartened that his best punches were having no effect, signalled defeat.

The rules of Onomastos were strict: No wrestling, grappling, kicking nor biting were allowed, and the contest ended when one combatant was knocked out or signalled submission It was this last rule, according to Plutarch, that had boxing banned in Sparta by its philosopher-king Lycurgus, since Spartans never surrendered. It was also strictly forbidden to intentionally kill an adversary, on pain of losing the match. Rhodes, Aegina, Arcadia and Elis produced most of the Olympic victors in boxing.

Onomastos held his title until 672 BC, when, in the 27th Olympic games, Diappos from Kroton was named Champion. The title changed hands again in 648 BC, when Komaios from Megara took the title. There were many great champions in the years that followed, but only one – Tisandros – was able to match Onomastos’ record 4 consecutive Olympic titles, and it was not matched again until the modern era.

Later, brutality gave way to technique and defence was valued more highly than attack. Matches became more lengthy, and records exist of some bouts lasting two days time. The zenith of this philosophy was reached in Melankomas, of whom Dio Chrysostum wrote in the 1st Century:

“Although he met so many antagonists and such good ones, he went down before none of them, but was himself always victorious… He won all his victories without being hit himself or hitting his opponent, so far superior was he in strength and in his power of endurance. For often he would fight throughout the whole day, in the hottest season of the year, and although he could have more quickly won the contest by striking a blow, he refused to do it, thinking that it was possible at times for the least competent boxer to overcome by a blow the very best man, if the chance for making it were offered; but he held that it was the truest victory when he forced his opponent, although uninjured, to give up because of his whole body, and not simply the part of his body that was struck…”

When Sulla plundered Olympia in 80 BC, the Greek Olympic tradition effectively ended, although boxing was evidently in vogue in very ancient times in Italy, and Greek or ‘provincial’ athletes were taken to Rome to compete. During the Republic, boxing was cultivated as a gentlemanly exercise, but contests increased in violence and depravity at the dawn of the Empire. Tacitus wrote that the emperor Caligula imported the best Campanian and African pugilists for the gladiatorial games. The sport remained popular in Italy throughout the reign of Nero but eventually boxing fell by the wayside in favour of more brutal pursuits.

... this is followed by a list of Olympic victors in the sport.