Res Gestae

Its first colour, so far as mortal eye can discern, is yellow, the second

It shows this combination of beautiful colours, as earthborn minds conceive, for the reason that its first part, corresponding in colour with the surrounding air, appears paler; the second is tawny, that is, somewhat more vivid than yellow; the third is red, because it is exposed to the brightness of the sun, and in proportion to alternation in the air absorbs its brilliance most purely, being just opposite;[*](I.e. the air is so affected by contact with the first two bands that it becomes more receptive of the effect of the sun’s rays.) the fourth is violet, because receiving the brightness of the sun’s rays with a thick rain of spray glittering between, through which it rises, it shows an appearance more like fire; and that colour, the more it spreads, passes over into blue and green.

Others think that the form of the rainbow appears to earthly sight when the rays of the sun penetrate a thick and lofty cloud and fill it with clear light. Since this does not find an outlet, it forms itself into a mass and glows from the intense friction; and it takes the colours nearest to white from the sun higher up, but the greenish shades from resemblance to the cloud just above it. The same thing usually happens with the sea, where the waters that dash upon the shore are white, and those further out without any admixture are blue.

And since the rainbow is an indication of a change of weather (as I have said), from sunny skies bringing up masses of clouds, or on the contrary changing an overcast sky to one that is calm and

For these and similar reasons the emperor wavered between hope and fear, since the severity of winter was drawing near and attacks were to be looked for in that trackless region, while also he feared mutiny of the exasperated soldiers. Besides this, his anxious mind was tormented by the thought that when, so to speak, the door of a rich house was open before him, he was returning without success.