In the year 732 AD, the new religion of Islam ruled throughout most of the known world. From Persia to Northern Spain, Muslim armies confidently marched forward with an irresistible force that had led to one hundred years of victories over all who opposed the spread of their militant faith. The warriors of Islam viewed all lands free of their control as the world of darkness, and a century of jihad to expand the light of Allah had known only success. The Pyrenees Mountains, an ancient barrier between Spain and France, had been breached by eighty thousand warriors under the command of Abd...