29. Others think that the rainbow is caused by the rays of the sun becoming infused into some dense cloud, and pouring into it a liquid light, which, as it can find no exit, falls back upon itself, and shines the more brilliantly because of a kind of attrition; and receives those hues which are most akin to white from the sun above; its green hues from the cloud under which it lies, as often happens in the sea, where the waters which beat upon the shore are white, and those farther from the land, which, as being so, are more free from any admixture, are blue. 30. And since it is an indication of a change in the atmosphere (as we have already said), when in a clear sky sudden masses of clouds appear, or on the other hand, when the sky changed from a gloomy look to a joyful serenity, therefore we often read in the poets that Iris is sent from heaven when a change is required in the condition of any present affairs. There are various other opinions which it would be superfluous now to enumerate, since my narration must hasten back to the point from which it digressed. 31. By these and similar events the emperor was kept wavering between hope and fear, as the severity of winter was increasing, and he suspected ambuscades in the country, which was destitute of roads; fearing also, among other things, the discontent of the exasperated soldiers. And it further goaded his unquiet spirit to return balked of his purpose, after, as it were, the door of the rich mansion was opened to him. 32. However, giving up his enterprise as fruitless, he returned into the unwelcome Syria, to winter at Antioch, after having suffered a succession of melancholy disasters. For, as if some unfriendly constellation so governed events, Constantius himself, while warring with the Persians, was always attended by adverse fortune; on which account he hoped at least to gain victories by means of his generals; and this, as we remember, usually happened. [109] "The minute interval which may be interposed between the _hyeme adultâ_ and the _primo vere_ of Ammianus, instead of allowing a sufficient space for a march of three thousand miles, would render the orders of Constantius as extravagant as they were unjust; the troops of Gaul could not have reached Syria till the end of autumn. The memory of Ammianus must have been inaccurate, and his language incorrect."--Gibbon, c. xxii. [110] According to Erdfurt, this legion was so named from its contumacious and mutinous disposition. [111] The Gentiles were body-guards of the emperor, or of the Cæsar, of barbarian extraction, whether Scythians, Goths, Franks, Germans, &c. [112] It may be remarked that Ammianus continually uses the words Persian and Parthian as synonymous. [113] Santon is near Cleves. BOOK XXI. ARGUMENT.