According to Arnold J. Toynbee, Mehmed and his immediate successors could thus be seen as "being as much a regenerator of the Byzantine Empire as its executioner".[23] Under Mehmed's successor Bayezid II (r. 1481–1512), basileus entered official usage.[20][24] Bayezid, his successor Selim I (r. 1512–1520) and Selim's successor Suleiman I (r. 1520–1566) all used basileus as their primary title in Greek-language documents.[25][24] Mehmed's kayser-i Rûm also became an integral part of the Ottoman imperial title.[26] When issuing documents in Serbian, Mehmed II, Bayezid II and Selim I are typically referred to under the title "great and mighty tsar", in this case deriving from their use of kayser.[27] In addition to adopting various titles, the Byzantine-oriented political identity of the early Ottoman sultans after 1453 also manifested itself in an increase in protocols, court ceremonies, architecture and symbols borrowed from Byzantium.[14] Both Selim and Suleiman at times employed the style "Emperor of Constantinople",[28] the title previously commonly used in diplomacy for the Byzantine emperors by Western Europeans.[29] Suleiman sometimes used the extended version "Emperor of Constantinople and Trebizond".[30] In Turkish, "Emperor of Constantinople" was rendered as padişah-i Kostantiniye.