In many cases the Carolingian monarchs rendered their signets, set with antique gems, significant of their own personality by having their names engraved around the setting. In this way Carloman (741–747) utilized an antique gem showing a female bust with hair tied in a knot, while Charlemagne’s choice was a gem engraved with the head of Marcus Aurelius; at a later time he substituted for this one bearing the head of the Alexandrian god Serapis. It is noteworthy that there is a great likeness between the portraits of Antoninus Pius and the type chosen for Serapis. Louis I, le Debonnaire (814–840), selected a portrait of Antoninus Pius, and his son, Lothaire, Roman emperor, 840–855 A.D., a gem with Caracalla’s head, the choice being no inappropriate one in view of Lothaire’s weak and treacherous character. Rev. C. W. King conjectures that the selection of the particular head may have depended upon its resemblance, more or less close, to the features of the monarch, as even though the likeness should not be very exact, the work would surpass anything that the unskilful gem-cutters of this age could produce.[241] Of the seal of the Prophet Mohammed, we are told by Ibn Kaldoun that when he was about to send a letter to the Emperor Heraclius, his attention was called to the fact that no letter would be received by a foreign potentate unless it bore the impression of the Prophet’s seal. Mohammed therefore had a seal made of silver, bearing the inscription “_Mohammed rasûl Allah_,” “Mohammed the Apostle of God”; these three words, according to Al-Bokhari, were disposed in three lines. The Prophet made use of this seal and forbade the making of any one like it. After his death it was employed by his successors, Abu Bekr, Omar and Othman, but the last-named unluckily let it fall from his hand into the well of Aris, whose depth it had never been possible to measure. A duplicate was executed to replace the original, but its loss was greatly deplored, and was looked upon as a possible presage of ill-fortune.[242] The title inscribed upon it was prouder in its simplicity than that assumed by any other ruler, not excepting those who claimed for themselves a divine ancestry, or divine attributes. These could at most pretend to rank as divinities of a lower order, while Mohammed claimed to be the mouthpiece of the one and only God. Burton writes that it is “a tradition of the Prophet” that the carnelian is the best stone for a signet ring, and this is still the usage among Mohammedans in the Orient. In the Arabian tale entitled “History of Al Hajjaj ben Yusuf and the Young Sayyed,” we read that the signet should be of carnelian because the stone was a guard against poverty.[243]