Excerpts from Books and Wikipedia
"In 807, al-Rashid granted Charlemagne yet another proof of the Frankish king's high place in the Christian hierarchy. He agreed to make a decree that protected the Christian holy sites in Jerusalem, which was under Arab governance: Christian pilgrims would be allowed, without restriction, to visit the Church of the Holy Sepulchre . . . and the other landmarks of their faith." [Bauer: Medieval World, p. 398]
"'Arab scholars were studying Aristotle,' writes Professor Phillip Hitti, 'when Charlemagne and his lords were learning to write their names. Scientists in Cordova, with their seventeen great libraries, one alone of which included more than 400,000 volumes, enjoyed luxurious baths at a time when washing the body was considered a dangerous custom at the University of Oxford.'" [Balyuzi: Muhammad and the Course of Islam, p. 287]