Charles always emphasised his royal rank, but did not adopt "imperial rhetoric". His renowned justiciar, Marino de Caramanico, developed a new political theory. Traditional interpretators of Roman law were convinced that the Holy Roman Emperors had a monopoly on law-making. In contrast with them, Caramanico stated that an emperor could not claim sovereignty over a king and emphasized Charles full competence to issue decrees. To promote legal education Charles paid high salaries20–50 ounces of gold in a yearto masters of law at the University of Naples. Masters of medicine received similar remunerations, and the university became a principal centre of medical science. Charles' personal interest in medicine grew during his life and he borrowed Arabic medical texts from the rulers of Tunis to have them translated. He employed at least one Jewish scholar, Moses of Palermo, who could translate texts from Arabic to Latin. Muhammad ibn Zakariya al-Razi's medical encyclopaedia, known as , was one of the books translated at Charles' order.