The King's role was to protect his people from enemies. In ancient Assyria, this was symbolized in the lion hunt, when the king went out to kill lions.
Lions were not uncommon in the Ancient Near East. King Ashurbanipal of Assyria noted that the hills abounded with lions who were killing cattle and humans alike.
It appears, though that the king had the lions caught for him, and brought to some sort of arena, where he could hunt the lions without having to go out and chase them.
This frieze is from the royal palace of Ashurbanipal, exhibited in the British Museum London.