An article came through the Byzans-L listserv linking Tony Blair to the emperor Heraclius, but in hunting around on the author’s dubious version of Heraclius’ interactions with Islam, I found this interesting account:
Now the Emperor was at this time at Hims, performing a pedestrian journey, in fulfillment of the vow which he had made, that, if the Romans overcame the Persians, he would travel on foot from Constantinople to Aelia (Jerusalem). So having read the letter, he commanded his chief men to meet him in the royal camp at Hims. And thus he addressed them: – ‘Ye chiefs of Rome! Do you desire safety and guidance, so that your kingdom shall be firmly established, and that ye may follow the commands of Jesus, Son of Mary?’ ‘And what, O King! shall secure us this?’ ‘Even that ye follow the Arabian Prophet,’ siad Heraclius. Where-upon they all started aside like wild asses of the desert, each raising his cross and waving it aloft in the air. Whereupon Heraclius despairing of their conversion, and unwilling to lose his kingdom, desisted, saying that he had only wished to test their constancy and faith, and that he was now satisfied by this display of firmness and devotion. The courtiers bowed their heads, and so the Prophet’s despatch was rejected (Katibu ‘l-Waqidi)
When I read this I thought of Agamemnon in reverse, testing the mettle of the assembled Greeks with a false offer to give up and go home. As this Arabic version has it, Heraclius wanted to convert, but bowed to the will of his followers.