In which year did Boxing Rings go from "Three "ropes to "Four" ropes ?

[Caractacus]

And why ?
ever notice that watching old boxing matches on film
then watching later boxing matches taped on video ?
I'm guessing around 1968 ?
Thats why all those great old classic ring action photographs from ringside
had been better and more memorable when
there was only three ropes seperating between the boxers and photographers.

[Controversial]

Not sure but I wonder if it coincided with the TV age to make it easier to film.