The relic did not long continue in the place to which the valour and piety of Heraclius had restored it, but was doomed to undergo still further vicissitudes of fortune. Only eight years afterwards (A.D. 636,) an army of Arabs, the new and fervent proselytes of Mahomet, invaded Palestine. At the battle of Yermuck, the imperial forces were totally routed, and Heraclius, downcast and dismayed, returned to Constantinople, bearing with him, as a source of consolation, the invaluable fragment, whose alleged miraculous powers were never exerted for its own protection.[9] It is rarely that, when a sovereign despairs of success, his subjects have the courage (it would, perhaps, be termed the disloyal presumption) to prolong their resistance; but the inhabitants of Jerusalem were animated by religious zeal and local associations, and did not, till after a doubtful siege of several months, yield the holy city to the Saracens. The event soon justified the prudent foresight of Heraclius in removing the Cross from the danger of Mahometan masters. The Caliph of Omar experienced some difficulties in the construction of a mosque at Jerusalem: he immediately supposed those difficulties to be supernatural, and, by the advice of the Jews, destroyed a great number of the neighbouring crosses; so that it seems certain that the wood of the real crucifixion could still less have escaped the effects of his ignorant fanaticism.[10] At Constantinople, on the contrary, it was preserved with the utmost veneration in the metropolitan church of St. Sophia, and the honours paid to it are attested and described by the father of English historians.[11] Never, but on the three most solemn festivals of the year, was its costly case unclosed. On the first day, it received the adoration of the emperor and principal officers of state; on the next, the empress and chief ladies repeated the same ceremony; and the bishops and clergy were admitted on the third. While exposed to view on the altar, a grateful odour pervaded the whole church, and a fluid resembling oil distilled from the knots in the wood, of which the least drop was thought sufficient to cure the most inveterate disease. This precious fluid is also mentioned by Pope Gregory, the Great, in one of his letters to Leontius. "I have received your present," writes the Pope, "some oil of the Holy Cross and some wood of aloes, of which the one confers blessing by its very touch, and the other, when burnt, diffuses a pleasant perfume."[12]