During the first part of his caliphate, Abubekr was engaged in suppressing revolts in different parts of the peninsula. These commotions quieted, he was free to carry out the last injunction of the Prophet to his followers, which enjoined them to spread his doctrines by the sword, till all men had confessed the creed of Islam, or consented to pay tribute to the Faithful. THE CONQUEST OF SYRIA.--The country which Abubekr resolved first to reduce was Syria. A call addressed to all the Faithful throughout Arabia was responded to with the greatest alacrity and enthusiasm. From every quarter the warriors flocked to Medina, until the desert about the city was literally covered with their black tents, and crowded with men and horses and camels. After invoking the blessing of God upon the hosts, Abubekr sent them forward upon their holy mission. Heraclius made a brave effort to defend the holy places against the fanatical warriors of the desert, but all in vain. His armies were cut to pieces. Seeing there was no hope of saving Jerusalem, he removed from that city to Constantinople the True Cross, which he had rescued from the Persians (see p. 390). "Farewell, Syria," were his words, as he turned from the consecrated land which he saw must be given up to the followers of the False Prophet. THE CONQUEST OF PERSIA (632-641).--While one Saracen army was overrunning Syria, another was busy with the subjugation of Persia. Enervated as this country was through luxury, and weakened by her long wars with the Eastern emperors, she could offer but feeble resistance to the terrible energy of the Saracens. Soon after the conquest of Persia, the Arabs crossed the mountains that wall Persia on the north, and spread their faith among the Turanian tribes of Central Asia. Among the most formidable of the clans that adopted the new religion were the Turks. Their conversion was an event of the greatest significance, for it was their swords that were destined to uphold and to spread the creed of Mohammed when the fiery zeal of his own countrymen should abate, and their arms lose the dreaded power which religious fanaticism had for a moment imparted to them.