Archaeological excavations show that the city may have grown significantly during the rule of the Persian Achaemenid Empire in the 6th century BCE. In 516 BCE, Darius I embarked on a campaign to conquer Central Asia, Ariana and Bactria, before marching onto what is now Afghanistan and northern Pakistan. Emperor Darius spent the winter of 516-515 BCE in the Gandhara region surrounding Taxila, and prepared to conquer the Indus Valley, which he did in 515 BCE, after which he appointed Scylax of Caryanda to explore the Indian Ocean from the mouth of the Indus to the Suez. Darius then returned to Persia via the Bolan Pass. The region continued under Achaemenid suzerainty under the reign of Xerxes I, and continued under Achaemenid rule for over a century.