M. Tullius Cicero Pro Fonteio 21

[21]
  But the Gauls deny this. But the circumstances of the case and the force of arguments prove it. Can then a judge refuse belief to witnesses? He not only can, but he ought, if they are covetous men, or angry men, or conspirators, or men utterly void of religion and conscience. In fact, if Marcus Fonteius is to be considered guilty just because the Gauls say so, what need have I of a wise judge? what need have I of an impartial judge? what need is there of an intelligent advocate? For the Gauls say so. We cannot deny it. If you think this is the duty of an able and experienced and impartial judge, that he must without the slightest hesitation believe a thing because the witnesses say it; then the Goddess of Safety herself cannot protect the innocence of brave men. But if, in coming to a decision on such matters, the wisdom of the judge has a wide field for its exercise in considering every circumstance, and in weighing each according to its importance, then in truth your part in considering the case is a more important and serious one than mine is in stating it.