The Annals and the Histories · Ann. 6.37

Vitellius, as soon as Artabanus had fled and his people were inclined to have a new king, urged Tiridates to seize the advantage thus offered, and then led the main strength of the legions and the allies to the banks of the Euphrates. While they were sacrificing, the one, after Roman custom, offering a swine, a ram and a bull; the other, a horse which he had duly prepared as a propitiation to the river-god, they were informed by the neighbouring inhabitants that the Euphrates, without any violent rains, was of itself rising to an immense height, and that the white foam was curling into circles like a diadem, an omen of a prosperous passage. Some explained it with more subtlety, of a successful commencement to the enterprise, which, however, would not be lasting, on the ground, that though a confident trust might be placed in prognostics given in the earth or in the heavens, the…

Cornelius Tacitus · trans. Church & Brodribb, 1876
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