Kaleb I of Aksum was probably encouraged to aggressively enlarge his empire by Justin. Contemporary chronicler John Malalas reported that Byzantine merchants were robbed and killed by the Jewish King of the south Arabian Kingdom of Himyar, causing Kaleb to claim, "You have acted badly because you have killed merchants of the Christian Romans, which is a loss both to myself and my kingdom." Himyar was a client state of the Sassanian Persians, perennial enemies of the Byzantines. Kaleb invaded Himyar, vowing to convert to Christianity if successful, which he was in 523. Justin thus saw what is now Yemen pass from Sassanian control to that of an allied and Christian state.