213 His brother, =Artabanus (IV)=, appears as a claimant of the throne. Civil war. 215 Caracalla demands the surrender of Tiridates, brother of Vologases IV, who has taken refuge with Vologases V. The latter refuses to give him up. Caracalla declares war, and the exile is delivered up. Artabanus gains the upper hand and holds Ctesiphon. Caracalla declares war on Artabanus on the latter’s refusal to give his daughter to the Roman emperor. 216 The Romans penetrate to Arbela. 217 On death of Caracalla an immense Parthian force invades Mesopotamia. Macrinus defeated and purchases peace. 222 Artabanus replaces his brother over the whole of Parthia. 224 Ardashir, the Sassanian king of Persis (or Persia), invades Parthia, taking several cities. 227 Battle of Hormizdjan. Victory of Ardashir and death of Artabanus. 228 Ardashir completes his conquest. End of the Parthian empire. THE EMPIRE OF THE SASSANIDS (228-651 A.D.) While the Arsacids were ruling their kingdom and lording it over the minor kings of the neighbouring country, the rulers of Persis (or Persia proper) seem to have occupied an isolated position and not been included in the Parthian empire. At the beginning of the third century A.D. the kings of Persia have lost all power of keeping the empire together; all the land is ruled by a number of local potentates. One of these is Pabak, son and descendant of a certain Sasan of Khir. Pabak conquers considerable territory beyond his own dominions. On his death the succession of Shapur or Sapor, the eldest son, is disputed by Ardashir, a younger son. Sapor dies suddenly and Ardashir puts his other brother to death, and settles himself on his throne in 211 or 212 A.D. About 224 he invades the land of the “great king” Artabanus IV of Parthia, and by 228 the conquest is complete and the title of “great king” devolves upon Ardashir. He makes his capital at Ctesiphon. 228 Foundation of the Sassanian empire by =Ardashir= or =Artaxerxes=. He passes his reign in extending and consolidating his empire. 236-238 War with Rome. Nisibis and Carrhæ taken. 241 Death of Ardashir. His son =Shapur= or =Sapor I= succeeds. 242 Sapor penetrates to Antioch but is driven back by the Romans. 244 Philippus concludes a humiliating peace with Sapor. Peace reigns until 251 when Sapor invades Armenia and puts the king to flight. The Persians now make repeated invasions of Syria. 258 The Roman emperor Valerian takes the field against the Persians.