Roger had now become one of the greatest kings in Europe. At Palermo, he gathered round him distinguished men of various races, such as the famous Arab geographer Muhammad al-Idrisi and the Byzantine Greek historian Nilus Doxopatrius. The king welcomed the learned and practised toleration towards the several creeds, races and languages of his realm. To administer his domain he hired many Greeks and Arabs, who were trained in long-established traditions of centralized government. He was served by men of diverse nationality, such as the Englishman Thomas Brun, a "kaid" of the "Curia" and, in the fleet by two Greeks, first Christodulus and then George of Antioch, whom he made in 1132 "ammiratus ammiratorum" or "Emir of Emirs", in effect prime vizier. (This title later became the English word admiral). Roger made Sicily the leading maritime power in the Mediterranean. Roger II had a kingdom where a Muslim scholar such as al-Idrisi could draw from a variety of intellectual traditions, because Sicily is positioned in the center of the Mediterranean and was a major stopping point for people traveling across the Mediterranean. Sicily had been run by several different groups in its history and Sicily under Roger II was tolerant of other religions.