 On 29 July 238, Pupienus and Balbinus were killed by the Praetorian Guard, who proclaimed Gordian III sole emperor.When the Sassanids invaded the Roman Empire in 241, occupying the province of Syria and capturing Antioch and Carrhae, Gordian III sent Timesitheus to counterattack.He recaptured the cities and won a decisive victory at Battle of Resaena.