Plutarch, Camillus
Bernadotte Perrin, Ed.

4. As was to be expected in a long siege requiring many meetings for conference with the enemy, it fell out that a certain Roman became intimate and confidential with one of the citizens of Veii, a man versed in ancient oracles, and reputed wiser than the rest from his being a diviner. The Roman saw that this man, on hearing the story of the lake, was overjoyed and made mock of the siege. He therefore told him this was not the only wonder which the passing days had brought, but that other and stranger signs than this had been given to the Romans, of which he was minded to tell him, in order that, if possible, he might better his own private case in the midst of the public distresses. [2] The man gave eager hearing to all this, and consented to a conference, supposing that he was going to hear some deep secrets. But the Roman led him along little by little, conversing as he went, until they were some way beyond the city gate, when he seized him bodily, being a sturdier man than he, and with the help of comrades who came running up from the camp, mastered him completely and handed him over to the generals. [3] Thus constrained, and perceiving that fate's decrees were not to be evaded, the man revealed secret oracles regarding his native city, to the effect that it could not be captured until the Alban lake, after leaving its bed and making new channels for itself, should be driven back by the enemy, deflected from its course, and prevented from mingling with the sea.

[4] The Senate, on hearing this, was at great loss what to do, and thought it well to send an embassy to Delphi to consult the god. The envoys were men of great repute and influence, Cossus Licinius, Valerius Potitus, and Fabius Ambustus, who made their voyage and Came back with the responses of the god. One of these told them that certain ancestral rites connected with the so-called Latin festivals had been unduly neglected; another bade them by all means to keep the water of the Alban lake away from the sea and force it back into its ancient bed, or, if they could not effect this, by means of canals and trenches to divert it into the plain and dissipate it. On receipt of these responses the priests performed the neglected sacrifices, and the people sallied out into the fields and diverted the course of the water.