That force was not the determining factor in these conversions may be judged from the amicable relations that existed between the Christian and the Muslim Arabs. Muḥammad himself had entered into treaty with several Christian tribes, promising them his protection and guaranteeing them the free exercise of their religion and to their clergy undisturbed enjoyment of their old rights and authority. [52] A similar bond of friendship united his followers with their fellow-countrymen of the older faith, many of whom voluntarily came forward to assist the Muslims in their military expeditions in the same spirit of loyalty to the new government as had caused them to hold aloof from the great apostasy that raised the standard of revolt throughout Arabia immediately after the death of the Prophet. [53] It has been suggested that the Christian Arabs who guarded the frontier of the Byzantine empire bordering on the desert threw in their lot with the invading Muslim army, when Heraclius refused any longer to pay them their accustomed subsidy for military service as wardens of the marches. [54] In the battle of the Bridge (A.H. 13) when a disastrous defeat was imminent and the panic-stricken Arabs were hemmed in between the Euphrates and the Persian host, a Christian chief of the Banū Ṭayy sprang forward like another Spurius Lartius to the side of an Arab Horatius, to assist Muthannah the Muslim general in defending the bridge of boats which could alone afford the means of an orderly retreat. When fresh levies were raised to retrieve this disgrace, among the reinforcements that came pouring in from every direction was a Christian tribe of the Banū Namir, who dwelt within the limits of the Byzantine empire, and in the ensuing battle of Buwayb (A.H. 13), just before the final charge of the Arabs that turned the fortune of battle in their favour, Muthannah rode up to the Christian chief and said: “Ye are of one blood with us; come now, and as I charge, charge ye with me.” The Persians fell back before their furious onslaught, and another great victory was added to the glorious roll of Muslim triumphs. One of the most gallant exploits of the day was performed by a youth belonging to another Christian tribe of the desert, who with his companions, a company of Bedouin horse-dealers, had come up just as the Arab army was being drawn up in battle array. They threw themselves into the right on the side of their compatriots; and while the conflict was raging most fiercely, this youth, rushing into the centre of the Persians, slew their leader, and leaping on his richly-caparisoned horse, galloped back amidst the plaudits of the Muslim line, crying as he passed in triumph: “I am of the Banū Taghlib. I am he that hath slain the chief.” [55]