The 1867 Queensberry rules fixed three-minute rounds with a minute's rest, a timing convenient for the stopwatches of the day, and it never changed.
Competitors play speed chess, then box, then return to the board. You can win by checkmate or knockout.
In 1974 Muhammad Ali reclaimed the heavyweight title in Kinshasa at the age of 32, winning in front of 60,000 people at dawn.
