Iain is right about the pseudo-Thucydides quote about soldiers and scholars that appears from time to time. For all its ubiquity, I don’t think anyone has found a precise citation from his history that might suggest Thucydides wrote anything like that. It’s sort of like the pseudo-Plato quote, “Only the dead have seen the end of the war,” that is likewise often cited as the philosopher’s, but never with a particular dialogue and section number.