Albert Barnes Commentary 2 Chronicles 9:18

"nd there were six steps to the throne, with a footstool of gold, which were fastened to the throne, and stays on either side by the place of the seat, and two lions standing beside the stays." — 2 Chronicles 9:18 (ASV)

The footstool (not mentioned in Kings) was an essential appendage to an Eastern throne; it appears everywhere in Egyptian, Assyrian, and Persian sculptures.