Camillus (3.2-3.3)

Of the lakes, rivers, and streams of all sizes with which Italy abounds, some had failed utterly, others barely managed to hold out, and all the rivers ran low, between high banks, as was always the case in summer. But the Alban lake, which had its source and outlet within itself, and was girt about with fertile mountains, for no reason, except it be that heaven willed it, was observed to increase and swell until it reached the skirts of the mountains and gradually touched their highest ridges. All this rise was without surge or billow.

At first it was a prodigy for neighbouring shepherds and herdsmen. But when the volume and weight of water broke away the barrier which, like an isthmus, had kept the lake from the country lying below it, and a huge torrent poured down through the fields and vineyards and made its way to the sea, then not only were the Romans themselves dismayed, but all the inhabitants of Italy thought it a sign of no small evil to come. There was much talk about it in the army that was besieging Veii, so that even the besieged themselves heard of the calamity.