However , exhausting wars with Byzantium left the empire unready to face the Muslim armies from Arabia .
The Sassanid Dynasty revived the old Achaemenid traditions , including Zoroastrianism , as Ardashir had promised .
Exhausting wars with Byzantium left the empire unready to face the Muslim armies from Arabia .
The Sassanid Dynasty revived the old Achaemenid traditions , including Zoroastrianism , as Ardashir had promised .