Volagases III, who succeeded, had designs on Armenia, and in 162 A.D. expelled the Arsacid Sohæmus, who was a client of Rome, and made Pacorus king. The destruction of a Roman legion under the legate of Cappadocia (Ælius Severianus), who fell on his own sword, laid Cappadocia and Syria open to the Parthians. When late in the year Ælius Verus arrived from the capital he found the troops so demoralised by defeat that he was ready to offer peace; but when Volagases refused to treat, the able lieutenants whom Verus directed from Antioch soon changed the face of affairs. The war had two theatres, and was officially called the Armenian and Parthian War. Armenia was regained and Sohæmus restored (163, 164 A.D.), while Avidius Cassius drove Volagases from Syria in a bloody battle at Europus, and entering north Mesopotamia, took Edessa and Nisibis, though not without serious opposition. At length, deserted by his allies (the local kings, who were becoming more and more independent), Volagases abandoned Mesopotamia, and Cassius entered Babylonia, where, on a frivolous pretext, he gave up to rapine and the flames the friendly city of Seleucia, still the first city of the East, with four hundred thousand inhabitants. The destruction of Seleucia was a hideous crime, a mortal wound dealt to Eastern Hellenism by its natural protectors; that Cassius next, advancing to Ctesiphon, razed the palace of Volagases to the ground may, on the other hand, be defended as a symbolical act calculated more than anything else to impair the prestige of the Parthian with his oriental subjects. Cassius returned to Syria in 165 A.D., with his victorious army much weakened through the failure of the commissariat and by the plague, which, breaking out in Parthia immediately after the fall of Seleucia, spread over the whole known world. In the same year Martius Verus won hardly less considerable successes in Media Atropatene, then apparently a separate kingdom. The peace which followed in 166 A.D. gave Mesopotamia to Rome. This was the greatest of all wars between Rome and Parthia, alike in the extent of the lands involved and the energy of attack shown by the Parthians. Parthia, after this last effort, continued steadily to decline. THE DECAY OF PARTHIAN GREATNESS [Sidenote: [166-217 A.D.]] The Romans at the same time made an effort to compete with Parthia for the Chinese trade (especially in silk), which the latter had jealously kept in their own hands, and in 166 A.D. an envoy of An-thun (M. Antoninus) reached the court of the emperor Huan-ti, _via_ the sea and Tongking. But the effort to establish a direct trade with China was unavailing, and the trade still flowed in its old channels when a second Roman agent reached China in 226 A.D., a little before the fall of the Parthian Empire. The Chinese tell us that with India also the Parthians drove a considerable trade.