When two adversaries are of equal strength of character, the contest of wills is certain to be long and hard-fought.
Dr Brewer tells us that the reference is to the obstinate resistance of the Greek cities to Philip and his son Alexander, the Macedonian kings, who were also Greeks by descent. The proverb as given above has become so established that we cannot change it now, yet it is a misquotation. The correct version, in a play called The Rivals Queens by Nathaniel Lee, is ‘When Greeks join’d Greeks, then was the tug of war’.
The verb ‘to join’ means here ‘to fight’ and a tug is a decisive contest. The athletic event derives its name from this.
It should be noted that when we use the proverb we are not referring to battles long ago, but to a difference of opinion between two strong-minded men.