In 646, the year before the victorious Arabs advanced from Egypt to the subjugation of the western province, the African Church that had championed so often the purity of Christian doctrine, was stirred to its depths by the struggle against Monotheletism; but when the bishops of the four ecclesiastical provinces in the archbishopric of Carthage, viz. Mauritania, Numidia, Byzacena and Africa Proconsularis, held councils to condemn Monotheletism, and wrote synodal letters to the Emperor and the Pope, there were only sixty-eight bishops who assembled at Carthage to represent the last-mentioned province, and forty-two for Byzacena. The numbers from the other two dioceses are not given, but the Christian population had undoubtedly suffered much more in these than in the two other dioceses which were nearer to the seat of government. [357] It is exceedingly unlikely that any of the bishops were absent on an occasion that excited so much feeling, when zeal for Christian doctrine and political animosity to the Byzantine court both combined in stimulating this movement, and when Africa took the most prominent part in stirring up the opposition that led to the convening of the great Lateran Council of 648. This diminution in the number of the African bishops certainly points to a vast decrease in the Christian population, and in consideration of the numerous causes contributing to a decay of the population, too great stress even must not be laid upon the number of these, because an episcopal see may continue to be filled long after the diocese has sunk into insignificance. From the considerations enumerated above, it may certainly be inferred that the Christian population at the time of the Muhammadan invasion was by no means a large one. During the fifty years that elapsed before the Arabs assured their victory, the Christian population was still further reduced by the devastations of this long conflict. The city of Tripolis, after sustaining a siege of six months, was sacked, and of the inhabitants part were put to the sword and the rest carried off captive into Egypt and Arabia. [358] Another city, bordering on the Numidian desert, was defended by a Roman count with a large garrison which bravely endured a blockade of a whole year; when at last it was taken by storm, all the males were put to the sword and the women and children carried off captive. [359] The number of such captives is said to have amounted to several hundreds of thousands. [360] Many of the Christians took refuge in flight, [361] some into Italy and Spain, [362] and it would almost seem that others even wandered as far as Germany, judging from a letter addressed to the diocese of St. Boniface by Pope Gregory II. [363] In fact, many of the great Roman cities were quite depopulated, and remained uninhabited for a long time or were even left to fall to ruins entirely, [364] while in several cases the conquerors chose entirely new sites for their chief towns. [365]