In August of the same year another raid on his camels was attempted by the famished tribes of Nejd, and Mahomet sent an expedition under Maslama to chastise them, but the Muslim were overpowered by a superior force and most of their company slain. The Prophet vowed vengeance upon the perpetrators of this defeat when he should have the power to carry it out. And now the Meccan caravan, venturing once more to take the seaward road, so long barred to them, was plundered by Zeid at Al Is, thereby confirming Mahomet's hostile intentions towards the Kureisch, and ensuring their continued enmity. But reprisals on their part were impossible after the failure before Medina, and they suffered the outrage in silence. Mahomet was not content to rest upon his newly won security, but now determined to send out messengers and embassies to the rulers of surrounding lands, exhorting them to embrace Islam. This policy was to develop later into a regular system, but for the moment only one envoy was sent upon a hazardous mission to the Roman emperor, whose recent conquests in Persia had made him famous among the Arabs. The envoy was not permitted a quiet journey. At Wadi-al-Cora he was seized and plundered by the Beni Judzam, but his property afterwards restored by the influence of a neighbouring tribe allied to Mahomet, who knew something of the revenge meted out by the Prophet. As it was, as soon as he heard of it he despatched Zeid with 500 men, who fell upon the Beni Judzam and slaughtered many. When the expedition returned to Medina with the news, they found that the tribe in question had sent in its submission before the slaying of its members. The Judzam envoys demanded compensation. "What can be done?" replied Mahomet. "I cannot restore dead men to life, but the booty that has been taken I will return and give you safe escort hence." Mahomet's next enterprise was to send one of his chief warriors and wise men to Dumah to try and convert the tribe. They listened to his words and promises, and after a time, judging it was not alone to their spiritual, but also to their political welfare to follow this powerful leader, they embraced Islam, and received the protectorship of the Prophet. Zeid returned from the plunder of the Kureisch caravan and straightway set out upon several mercantile journeys, upon one of which he was set upon and plundered by the Beni Fazara, near Wadi-al-Cora. Swift retribution followed at the hands of Mahomet, who was not minded to see the expeditions that were securing the wealth of his land the prey of marauding tribes. Many barbarities were practised at the overthrow of the Beni Fazara, possibly as a salutary lesson to neighbouring tribes, lest they should presume to attempt like attacks.