Conflict resumed shortly after the overthrow of Parthian rule and Ardashir I's foundation of the Sasanian Empire. Ardashir (r. 226–241) raided Mesopotamia and Syria in 230 and demanded the cession of all the former territories of the Achaemenid Empire.* Dodgeon–Greatrex–Lieu (2002), I, 16</ref> After fruitless negotiations, Alexander Severus set out against Ardashir in 232 and finally repulsed him after one column of his army marched successfully into Armenia, while two other columns operated to the south and failed, mostly on account of physical hardship; the emperor celebrated a triumph in Rome.* Dodgeon–Greatrex–Lieu (2002), I, 24–28; Frye (1993), 124</ref> In 238–240, towards the end of his reign, Ardashir attacked again, taking several cities in Syria and Mesopotamia, including Carrhae, Nisibis and Hatra.