Why Is A Boxing Ring Square?

Well I can only imagine the most likely answer is, so that each boxer can go to his corner, and start  the fight from his corner. Where his trainer and manager are biting their nails and waiting to sponge him down, with that bloodstained sponge they always have at the ready ,while they shout incoherent orders into his punchdrunk ears.

If  the ring was round, it would be difficult to get the contestants to stop beating each other as they would not have a designated place.

The rings were originally round when they were Roman, and like the Coliseum in Rome, where built to seat the spectators around in stone seats and watch them fight it out to the death.
All this, for the enjoyment of the public. We've come a long way since then (or so they tell us ) and now we have corners to stop them killing each other, in the ring.