Three Checks to Autocracy
The supreme, god-like position of the Assyrian monarch was promoted and enhanced in a variety of practical ways. Access to the king by individuals was, at best, extremely difficult, and the long walk through the gates and corridors flanked by bull and lion colossi and stone reliefs depicting the king slaying and mutilating his enemies would overwhelm the visitor, as it was intended to do, with 'awesome splendour'.... The only mortal who could be regarded as an equal of the Assyrian king was a foreign king, whom the Assyrian monarch addressed as 'my brother', but even he was a potential subject of the 'king of kings'....
The Assyrian king enjoyed absolute power over the state, there being only three checks to his autocratic rule, religion, legal precedent, and the temper of his nobles and officials. The monarch was subject to religious belief and practice, and examples of royal attempts to depart therefrom are extremely rare. As to legal precedent, the king had to respect the traditional rights of individuals, such as property ownership, and of groups or institutions, such as tax exemptions granted to privileged cities. Finally he had to respect the mood of the upper classes or run the risk, as a few kings did, of revolution and regicide. Apart from these considerations, however; the king's will was supreme in all affairs of state. Indeed, in the legislative sphere he was not only the supreme but the sole legislator, his 'law-making' consisting of royal decrees. There was not even an assembly, as in Sumer, with which he might discuss a proposal, although he did seek advice from his various officials and sanction from the gods by means of omens. The king was presumably supreme judge, and he was definitely commander-in-chief of the army. In religion, although he was subject to commonly accepted beliefs and practices, as already mentioned, he was the high priest...of the god Ashur. This is in contrast to Babylonia where the high priest was not the same person as the king. Finally, even the economy was subject to his will, for in theory he owned all the land, and trade, both domestic and foreign, depended upon his sanction.
— The Cambridge Ancient History, volume III, part 2, p. 196