Soured by this failure, which modern historians consider the beginning of Achaemenid decline, Xerxes retired to Susa and Persepolis. He then furthered the depletion of the once-enormous resources he had gathered, through multiple taxation, by launching a vast construction program. At the capital city of Persepolis, Darius’ architects, working from a unified plan of great scope, had already begun construction on a gigantic terrace of the apadana (an audience hall), the Tripylon, a palace, and a treasury. When Xerxes became king, he had laid the enameled-brick facing on the exterior of the apadana and finished his father’s palace. Then he erected other monuments: his own palace, southeast of Darius’ and similar to it in plan, and a mysterious building called the harem by archaeologists—a line of small, identical rooms that may have been Xerxes’ treasury. He also undertook construction of the Hall of a Hundred Columns, or Throne Room, but he was able to finish only the paving and the base of the walls (the walls themselves and the decoration of this gigantic hypostyle hall were the work of Artaxerxes I). These buildings marked an evolution toward the colossal and toward a style that was perhaps more pretentious than that typical of Darius’ reign.

Little is known about the last years of Xerxes’ life. After his reversal in Greece, he withdrew into himself and allowed himself to be drawn into harem intrigues in which he was, in fact, only a pawn; thus, he disposed of his brother’s entire family at the demand of the queen. But in 465 bce he himself fell, together with his eldest son, under the blows of murderous members of his court, among them his minister Artabanus. Another son, Artaxerxes I, succeeded in retaining power.