This opera is set in Persia (present day Iran) in 480 BC and is very loosely based upon Xerxes I of Persia. Apart from the reported infatuation of King Xerxes with a plane tree and his reported construction of a bridge, this tale is pure supposition. Xerxes is engaged to Amatris, but wishes to marry Romilda, the daughter of his successful general. Romilda wants to marry Arsamenes, the brother of the King, but Atalanta - Romilda's sister - wants Arsamenes to be her husband.