Any history of late Assyrian art must be concerned primarily with relief carving. Some statues in the round have been found, but the comparative ineptitude of the majority of them suggests that this form of expression did not come naturally to Assyrian sculptors. Portal sculptures, which many would consider the most characteristic Assyrian art form, are not statues in the round but "double-aspect" reliefs (that is, they are meant to be seen from either the front or the side), apparently derived from a Hittite invention of the 14th century BC. These impressive guardian figures--usually human-headed bulls or lions--decorate the arched gateways and are sometimes supplemented by others set at right angles on the adjoining facades, their heads facing sideways. Each is composed from a single block of stone weighing up to 30 tons, roughly shaped in the quarry and then carved in situ.
The earliest slabs, from the 9th-century palaces of Ashurnasirpal II and his son Shalmaneser III at Nimrud, are about two metres high, with the design arranged in two superimposed registers separated by a band of cuneiform inscription. In those from later buildings, such as Sargon II's palace at Khorsabad, the individual sculptured figures reach a height of nine feet. The subjects of the designs on these reliefs are rarely related in any way to religion. Superstitious symbols do occasionally appear in the form of benevolent winged beings, or genies, but the primary purpose of the picture is the glorification of the king himself, either by scenes of ceremonial homage or by extended pictorial narratives of his achievements.
The most popular theme, giving rise to numerous variations, involves detailed scenes of military conquest and the ruthless suppression of revolt. These are often arranged episodically to represent successive events in the progress of a single campaign: the Assyrian army prepares for war; led by the king, it crosses difficult country on the way to attack a walled city; the city is taken, burnt, and demolished; the enemy leaders are punished with conspicuous brutality; and, finally, the victory is celebrated. Scenes such as these are distinguished above all by their stylistic vitality and fanciful detail. Animals as well as men are carefully observed and beautifully drawn. The principles of perspective as later defined by the Greeks are unknown, but attention is given to the relationship of figures in space and to devices for suggesting comparative distance.
In the 7th-century palaces of Sennacherib and Ashurbanipal at Nineveh, the reliefs suggest a reaction in favour of narrative and violent activity. The slabs are covered to their full height by complicated battle scenes in which the progress of the fighting is suggested by episodic repetition. Types of landscape are depicted schematically, and significant episodes or individuals are identified by a short inscription, without impairing the overall rhythm of the design. In the intervals between their military campaigns, Assyrian kings appear to have been much preoccupied with hunting, and scenes from the chase provided an alternative subject for the reliefs. Lions hunted with spears from a light chariot and herds of wild asses (onagers) or gazelles are subjects that stimulated the imagination and sensibility of the Assyrian artist. A contrast to these descriptive carvings is provided by the formal monumentality of the Assyrian rock reliefs, secular or religious devices carved on vertical rock faces in localities such as Bavian and Maltai to commemorate historical events that took place there.