Examination of urine was the key diagnostic tool of medieval medicine. Medical knowledge of urine and nearly everything else in medieval European medicine came from Arabic sources. The most important authority on uroscopy (examination and analysis of urine) was Isaac the Jew, whose 10th-century work in Arabic had been translated into Latin by an 11th-century author, Constantius Africanus, who was from North Africa and taught at the top-flight medical school in Salerno. Isaac in turn had expanded the earlier Greek compilation on urine by Theophilos, a Byzantine authority. This medical manuscript belonged to the Benedictine abbey in Malmesbury. The Benedictine monks formed an important sector of medieval medical scholarship and practice. The Isaac's treatise on urine, credited to Theophilos, begins with a historiated initial (first letter bearing a picture) of Theophilos examining a flask of urine. Two assistants or students stand at the ready with more flasks.