The Iliad 10.177–191

Now when they had joined the company of the sentinels as they were gathered together, they found not the leaders of the sentinels asleep, but all were sitting awake with their arms. And even as dogs keep painful watch about sheep in a fold, when they hear the wild beast, stout of heart, that cometh through the wood among the hills, and a great din ariseth about him of men and dogs, and from them sleep perisheth; even so from their eyelids did sweet sleep perish, as they kept watch through the evil night; for toward the plain were they ever turning if haply they might hear the Trojans coming on. At sight of them the old man waxed glad and heartened them, and spake and addressed them with winged words: Even so now, dear children, keep your watch, neither let sleep seize any man, lest we become a cause of rejoicing to our foes. So saying he hasted through the trench, and there followed with him