Like a lot of people, I'm an addict to the Danish TV drama The Killing. In a recent episode there was a subtitle reading "towing the line". I've no idea if there is an equivalent idiom in Danish, but in English this is not a nautical metaphor, as one might expect from "towing". It should be "toeing" the line, because it comes from boxing. When boxing was being established as a sport in the late eighteenth and early nineteenth centuries, a line would be drawn in the sand which the combatants had to come up to in order to be able to continue the contest. Hence "toeing the line" meant being in a fit mental and physical state to continue fighting.