The exact route taken by Odaenathus from Palmyra to Ctesiphon remain uncertain ; it is probably similar to the route emperor Julian took in 363 during his campaign against Persia . Using this route , Odaenathus would have crossed the Euphrates at Zeugma then moved east to Edessa followed by Carrhae then Nisibis ; here , he would have descended south along the Khabur River to the Euphrates valley and marched alongside the river 's left bank to Nehardea . After taking the city , he penetrated the Sassanian province of Asōristān and marched along the royal canal Naarmalcha towards the Tigris where the Persian capital stood .