of Assyria and Babylon. Later Assyrian rulers to use šar šarrāni include Esarhaddon (r. 681–669 BC) and Ashurbanipal (r. 669–627 BC). "King of Kings", as šar šarrāni, was among the many titles of the last Neo-Babylonian king, Nabonidus (r. 556–539 BC). Boastful titles claiming ownership of various things were common throughout ancient Mesopotamian history. For instance, Ashurbanipal's great-grandfather Sargon II used the full titulature of Great King, Mighty King, King of the Universe, King of Assyria, King of Babylon, King of Sumer and Akkad. Urartu and Media The title of King of Kings occasionally appears in inscriptions of kings of Urartu. Although no evidence exists, it is possible that the title was also used by the rulers of the Median Empire, since its rulers borrowed much of their royal symbolism and protocol from Urartu and elsewhere in Mesopotamia. The Achaemenid Persian variant of the title, , is Median in form which suggests that the Achaemenids may have taken it from the Medes rather than from the Mesopotamians. An Assyrian-language inscription on a fortification near the fortress of Tušpa mentions King Sarduri I of Urartu as a builder of a wall and a holder of the title King of Kings; Iran Achaemenid usage The Achaemenid Empire, established in 550 BC after the fall of the Median Empire, rapidly expanded over the course of the sixth century BC. Asia Minor and the Lydian kingdom was conquered in 546 BC, the Neo-Babylonian Empire in 539 BC, Egypt in 525 BC and the Indus region in 513 BC. The Achaemenids employed satrapal administration, which became a guarantee of success due to its flexibility and the tolerance of the Achaemenid kings for the more-or-less autonomous vassals. The system also had its problems; though some regions became nearly completely autonomous without any fighting (such as Lycia and Cilicia), other regions saw repeated attempts at rebellion and secession. Egypt was a particularly prominent example, frequently rebelling against Achaemenid authority and attempting to crown their own Pharaohs. Though it was eventually defeated, the Great Satraps' Revolt of 366–360 BC showed the growing structural problems within the Empire. The Achaemenid Kings used a variety of different titles, prominently Great King and King of Countries, but perhaps the most prominent title was that of King of Kings (rendered in Old Persian), recorded for every Achaemenid king. The full titulature of the king Darius I was "great king, king of kings,