Plutarch, Aratus
Bernadotte Perrin, Ed.

21. When all things were ready, Aratus ordered the rest of his forces to pass the night under arms, and taking with him four hundred picked men, few of whom knew what was on foot themselves, led them towards the gate of Corinth near by the temple of Hera. It was midsummer, the moon was at its full, and the night was cloudless and clear, so that they feared lest the gleam of their arms in the moonlight should disclose them to the sentinels. [2] But just as the foremost of them were near the wall, clouds ran up from the sea and enveloped the city itself and the region outside, which thus became dark. Then the rest of them sat down and took off their shoes, since men make little noise and do not slip if they are barefooted when they climb ladders; but Erginus, taking with him seven young men equipped as travellers, got unnoticed to the gate. [3] Here they slew the gate-keeper and the sentries who were with him. At the same time the ladders were clapped to the wall, and after getting a hundred men over in all haste, Aratus ordered the rest to follow as fast as they could; then he pulled his ladders up after him and marched through the city with his hundred men against the citadel, being already full of joy at his escape from detection and confident of success.

[4] A little farther on they encountered a watch of four men with a light; they were not seen by them, being still in the shade of the moon, but saw them coming up in the opposite direction. So they drew back a little for shelter beneath some walls and buildings, and set an ambush for the men. Three of them they killed in their attack, but the fourth, with a sword-wound in his head, took to flight, crying out that the enemy were in the city. [5] And presently the trumpets were sounding, the city was in an uproar over what was happening, the streets were full of people running up and down, many lights were flashing, some in the city below and some in the citadel above, and a confused shouting broke forth on all hands.