During the Middle Ages, the Christian world held a largely antagonistic view of Muhammad. This partly represented lack of knowledge about the Muslim prophet, but also stemmed from the claim that Islam had adopted an aggressive and violent approach to expanding its influence. Consequently, Christianity and Islam were secular and religious enemies throughout much of this era.
Early Middle Ages
The earliest (documented) Christian knowledge of Muhammad stems from Byzantine sources, written shortly after Muhammad's death in 632. In the Doctrina Jacobi nuper baptizati, a dialogue between a recent Christian convert and several Jews, one participant writes that his brother "wrote to [him] saying that a deceiving prophet has appeared amidst the Saracens". Another participant in the Doctrina replies about Muhammad: "He is deceiving. For do prophets come with sword and chariot?, ...[Y]ou will discover nothing true from the said prophet except human bloodshed". Though Muhammad is never called by his name, there seems to have been knowledge of his existence. It also appears that both Jews and Christians viewed him in a negative light. Other contemporary sources, such as the writings of the Patriarch Sophronius, show there was no knowledge of the Arabs having their own prophet or faith, and only remark that the (Muslim) Arab attacks must be a punishment for Christian sins.
Knowledge of Muhammad was available in Christendom from the time of the translation of a polemical work by John of Damascus, who coined the pejorative phrase "false prophet". and "was nearly always used abusively."  Another influential source was the Epistolae Saraceni or the “Letters of a Saracen” written by an Oriental Christian and translated into Latin from Arabic. From the 9th century onwards, highly negative biographies of Muhammad were written in Latin, such as the one by Alvarus of Cordoba proclaiming him the Anti-Christ.
The addition to Byzantine sources such as Eulogius of Cordova from the 9th century, Christendom also gained some knowledge of Muhammad through the Mozarabs of Spain such as Petrus Alfonsi, a Jew who converted to Christianity, in the 11th century. Later during the 12th century Peter the Venerable, who saw Muhammad as the precursor to the Anti-Christ and the successor of Arius, ordered the translation of the Qur'an into Latin and the collection of information on Muhammad so that Islamic teachings could be refuted by Christian scholars.
During the 13th century European biographers completed their work on the life of Muhammad in a series of works by scholars such as Pedro Pascual, Ricoldo de Monte Croce, and Ramon Llull in which Muhammad was depicted as an Antichrist while Islam was shown to be a Christian heresy Facts such as the Muslim belief that he was unlettered, that he married a wealthy widow, that in his later life he had several wives, that he ruled over a human community and was therefore involved in several wars, and that he died like an ordinary person in contrast to the Christian belief in the supernatural end of Christ's earthly life were all interpreted in the worst possible light.
Medieval scholars and churchmen held that Islam was the work of Muhammad who in turn was inspired by Satan. Muhammad was frequently calumnized and made a subject of legends taught by preachers as fact. For example, in order to show that Muhammad was the anti-Christ, it was asserted that Muhammad died not in the year 632 but in the year 666 - the number of the beast - in another variation on the theme the number "666" was also used to represent the period of time Muslims would hold sway of the land. A verbal expression of Christian contempt for Islam was expressed in turning his name from Muhammad to Mahound, the "devil incarnate". Others usually confirmed to pious Christians that Muhammad had come to a bad end. According to one version after falling into a drunken stupor he had been eaten by a herd of swine, and this was ascribed as the reason why Muslims proscribed consumption of alcohol and pork. Leggenda di Maometto is an example of those in which he is taught from childhood the black arts by a heretical Christian villain who escaped imprisonment by the Church to Arabia and set up a false religion by selectively choosing and perverting text from the Bible and the Old Testament to set up Islam. It also ascribed the Muslim holiday of Friday "dies veneris" (day of Venus) vs. the Jewish (Saturday) and the Christian (Sunday), to his followers depravity as reflected in their multiplicity of wives. A highly negative depiction of Muhammad as a heretic, false prophet, renegade cardinal, or founder of a violent religion also found its way into many other works of European literature, such as the chansons de geste, William Langland's Piers Plowman, and John Lydgate's The Fall of the Princes.
During the Middle Ages, especially in places where there was frequent Christian-Muslim conflict, it was popular to depict Muhammad being tortured by the demons in Hell. One such example is in Dante's The Divine Comedy in which Muhammad is in the ninth ditch of the eighth circle of hell, the realm for those who have caused schism; specifically, he was placed among the Sowers of Religious Discord. One common allegation laid against Muhammad was that he was an impostor who, in order to satisfy his ambition and his lust, propagated religious teachings that he knew to be false.
A more positive interpretation appears in the 13th century Estoire del Saint Grail, the first book in the vast Arthurian cycle, the Lancelot-Grail. In describing the travels of Joseph of Arimathea, keeper of the Holy Grail, the author says that most residents of the Middle East were pagans until the coming of Muhammad, who is shown as a true prophet sent by God to bring Christianity to the region. This mission however failed when Muhammad's pride caused him to alter God's wishes, thereby deceiving his followers. Nevertheless, Muhammad's religion is portrayed as being greatly superior to paganism.
The depiction of Islam in the Travels of Sir John Mandeville is also relatively positive, though with many inaccurate and mythical features. It is said that Muslims are easily converted to Christianity because their beliefs are already so similar in many ways, and that they believe that only the Christian revelation will last till the end of the world. The moral behaviour of Muslims at the time is shown as superior to that of Christians, and as a standing reproach to Christian society. 
Other Romantic depictions of Muhammad also began to appear from the 13th century onward, such as in Alexandre du Pont's Roman de Mahom, the translation of the Mi'raj, the Escala de Mahoma (“The Ladder of Muhammad”) by the court physician of Alfonso X of Castile and Leon and his son.
Some Christians also believed Muslims worshipped Muhammad giving rise to the term Mohammedan, while others simply believed he was a Christian heretic. Still others in medieval European literature often referred to Muslims as "pagans", or by sobriquets such as the paynim foe. These depictions such as those in the Song of Roland represent Muslims worshiping Muhammad (spelt e.g. 'Mahom' and 'Mahumet') as a god, and depict them worshiping various deities in the form of "idols", ranging from Apollo to Lucifer, but ascribing to them a chief deity known as "Termagant". Conversely, actual pagans, however long they antedate the birth of Muhammad, are shown as worshipping the same array of gods and as identical to Muslims in every respect.
When the Knights Templar were being tried for heresy reference was often made to their worship of a demon Baphomet, which was notable by implication for its similarity to the common rendition of Muhammad's name used by Christian writers of the time, Mahomet. All these and other variations on the theme were all set in the "temper of the times" of what was seen as a Muslim-Christian conflict as Medieval Europe was building a concept of "the great enemy" in the wake of the quickfire success of the Muslims through a series of conquests shortly after the fall of the Western Roman Empire, as well as the lack of real information in the West of the mysterious east.
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- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 "Muhammad." Encyclopædia Britannica. 2007. Encyclopædia Britannica Online. 10 Jan. 2007, .
- ↑ Esposito (1998) p.14
- ↑ Watt (1974) p.231
- ↑ Walter Emil Kaegi, Jr., "Initial Byzantine Reactions to the Arab Conquest", Church History, Vol. 38, No. 2 (Jun., 1969), p. 139-149, p. 139-142, quoting from Doctrina Jacobi nuper baptizati 86-87
- ↑ Walter Emil Kaegi, Jr., "Initial Byzantine Reactions to the Arab Conquest", Church History, Vol. 38, No. 2 (Jun., 1969), p. 139-149, p. 139-142
- ↑ Walter Emil Kaegi, Jr., "Initial Byzantine Reactions to the Arab Conquest", Church History, Vol. 38, No. 2 (Jun., 1969), p. 139-149, p. 139-141,
- ↑ Source: "The Fountain of Wisdom" (pege gnoseos), part II: "Concerning Heresy" (peri aipeseon)
- ↑ 8.0 8.1 8.2 8.3 Kenneth Meyer Setton (July 1, 1992). "Western Hostility to Islam and Prophecies of Turkish Doom". DIANE Publishing. ISBN 0-87169-201-5. pg 4-15
- ↑ 9.0 9.1 9.2 9.3 Kenneth Meyer Setton (July 1, 1992). "Western Hostility to Islam and Prophecies of Turkish Doom". DIANE Publishing. ISBN 0-87169-201-5. pg 1-5
- ↑ Reeves (2003), p.3
- ↑ 11.0 11.1 Watt, Montgomery, Muhammad: Prophet and Statesman. Oxford University Press, 1961. From p. 229.
- ↑ Lacy, Norris J. (Ed.) (December 1, 1992). Lancelot-Grail: The Old French Arthurian Vulgate and Post-Vulgate in Translation, Volume 1 of 5. New York: Garland. ISBN 0-8240-7733-4.
- ↑ The Travels of Sir John Mandeville, CHAPTER XV.
- ↑ Brewer's Dictionary of Phrase and Fable, "Termagant
- ↑ The definition of "Saracen" in Raymond de Peñafort's Summa de Poenitentia starts by describing the Muslims but ends by including every person who is neither a Christian nor a Jew.
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