 In 408, his father died and the seven-year-old boy became Emperor of the Eastern half of the Roman Empire.According to Procopius, the Sasanian king Yazdegerd I (399-420) was appointed by Arcadius as the guardian of Theodosius, whom Yazdegerd treated as his own child, sending a tutor to raise him and warning that enmity toward him would be taken as enmity toward Persia.Government was at first by the Praetorian Prefect Anthemius, under whose supervision the Theodosian land walls of Constantinople were constructed.