 His departure stimulated the writing of Julian's oration, "Consolation Upon the Departure of Salutius".In the fourth year of Julian's stay in Gaul, the Sassanid Emperor, Shapur II, invaded Mesopotamia and took the city of Amida after a 73-day siege.In February 360, Constantius II ordered more than half of Julian's Gallic troops to join his eastern army, the order by-passing Julian and going directly to the military commanders.