Susa is the capital of Persia, which according to the chroniclers was founded by the brother of Memnon; and it is called Susa because it borders on the river Susa, which is the location of the royal palace of Cyrus. This was known for its bright and colorful stone, along with its gold columns, its ponds, and its gems; and it also contained a likeness of the heavens inlaid with shining stars, and other things that the human mind finds difficult to comprehend. And it was there, we are told, that the king in question would stage for his subject peoples a grand feast that featured impressive accouterments and a wealth of riches.
Source: Commentary on Esther