may have been exaggerated by his followers, writing that "other" Arab leaders "in other locations" had preceded Muhammad in attacking the weakened Byzantine and Persian empires, but these had been "airbrushed out of history by later Muslim writers". Hoyland and other historians argue that the original Arab invaders were not all Muslims. Minority views A minority of historians have posited that Muhammad may be mythical. In the 2003 book Crossroads to Islam, Yehuda D. Nevo and Judith Koren advanced a thesis, based on an extensive examination of archaeological evidence from Negev desert from the early Islamic period, that Muhammad may never have existed, with monotheistic Islam only coming into existence some time after he is supposed to have lived. This has been described as "plausible or at least arguable" by David Cook of Rice University, but also compared to Holocaust denial by historian Colin Wells, who suggests that the authors deal with some of the evidence illogically. In 2007, Karl-Heinz Ohlig suggested that the person of Muhammed was not central to early Islam at all, and that at this very early stage Islam was in fact an Arabic Christian sect which had objections to the concept of the trinity, and that the later hadith and biographies are in large part legends, instrumental in severing Islam from its Christian roots and building a full-blown new religion. In 2008, Sven Kalisch, a former Muslim convert and Germany's first professor of Islamic theology, also questioned whether the prophet Muhammad existed. In 2011, Hans Jansen, a Dutch scholar, expressed similar views. See also Ashtiname of Muhammad Reliability of the Quran Historicity of Jesus Historicity of the Bible Historiography of early Islam Islam: The Untold Story Muhammad's letters to the heads of state Phantom time hypothesis Relics of Muhammad Soviet Orientalist studies in Islam Seeing Islam as Others Saw It Notes Citations References Muhammad Muhammad