The London Prize Ring Rules, 1838, were expanded upon a list of rules drafted by Britain's Jack Broughton in 1743, governing the conduct of prizefighting/boxing for over 100 years. The rules were again revised in 1853.
Fights under these rules, typically fought with bare knuckles, also allowed for holds, throws of the opponent and, within limits, spiked shoes. Also included were provisions dealing with how wagers would be resolved if various events such as interference by the law, darkness, or cancellations occurred. In contrast with modern boxing rules based upon the Marquess of Queensberry rules, a round ended with a man downed by punch or throw, whereupon he was given 30 seconds to rest and eight additional seconds to "come to scratch" or return to the center of the ring where a "scratch line" was drawn and square off with his opponent once more.
Consequently, there were no round limits to fights. When a man could not come to scratch, he would be declared loser and the fight would be brought to a halt, unless broken up beforehand by crowd riot, police interference or chicanery. Fights could also end if both men were willing to accept that the contest was a draw. While fights could have enormous numbers of rounds, the rounds in practice could be quite short with fighters pretending to go down from minor blows to take advantage of the 30-second rest period.   [major info via www.reference.com]

This is yet a bit milder than an early Greek form when opponents sat on stones, taking turns at pummeling one another until one of the stoned parties fell off his rock - er, stone.