Shushan (Susa): Capitol of the Medo-Persian Empire
Source: Nav
Esther 1:2, 3
In those days King Xerxes sat on his royal throne in the citadel of Susa. / In the third year of his reign, Xerxes held a feast for all his officials and servants. The military leaders of Persia and Media were there, along with the nobles and princes of the provinces.
Esther 8:15
Mordecai went out from the presence of the king in royal garments of blue and white, with a large gold crown and a purple robe of fine linen. And the city of Susa shouted and rejoiced.