24. But when the approach of evening broke off the conflict, and the two sides separated to snatch a brief repose, the emperor, after due reflection, resolved to change his plans. Although many reasons of great urgency pressed him to force on the destruction of Phoenice, as of a fortress which would prove an impregnable barrier to the inroads of the enemy, yet the lateness of the season was an objection to persevering any longer. He determined, therefore, while he preserved his position, to carry on the siege for the future by slight skirmishes, thinking that the Persians would be forced to surrender from want of provisions, which, however, turned out very different. 25. For while the conflict was proceeding sharply, the heavens became moist, and watery clouds appeared with threatening darkness; and presently the ground got so wet from continual rain, that the whole country was changed into an adhesive mud (for the soil is naturally rich), and every plan was thrown into confusion; meantime, thunder with incessant crashes and ceaseless lightning filled men's minds with fear. 26. To these portents were added continual rainbows. A short explanation will serve to show how these appearances are formed. The vapours of the earth becoming warmer, and the watery particles gathering in clouds, and thence being dispersed in spray, and made brilliant by the fusion of rays, turn upwards towards the fiery orb of the sun and form a rainbow, which sweeps round with a large curve because it is spread over our world, which physical investigations place on the moiety of a sphere. 27. Its appearance, as far as mortal sight can discern, is, in the first line yellow, in the second tawny, in the third scarlet, in the fourth purple, and in the last a mixture of blue and green. 28. And it is so tempered with this mixed beauty, as mankind believe, because its first portion is discerned in a thin diluted state, of the same colour as the air which surrounds it; the next line is tawny, that is a somewhat richer colour than yellow; the third is scarlet, because it is opposite to the bright rays of the sun, and so pumps up and appropriates, if one may so say, the most subtle portion of its beams; the fourth is purple, because the density of the spray by which the splendour of the sun's rays is quenched shines between, and so it assumes a colour near that of flame; and as that colour is the more diffused, it shades off into blue and green.