Relations between the Roman and Iranian states were established c. 92 BC. It was in 69 BC that the two states clashed for the first time; the political rivalry between the two empires would dominate much of Western Asia and Europe until 628. Initially commencing as a rivalry between the Parthians and Rome, from the 3rd to mid-7th centuries the Roman Empire (later the Byzantine Empire) and its rival Sassanid Persia were recognized as two of the leading powers in the world. Relations during the Republic The first direct contact between the Roman Republic and the Parthians was c. 92 BC, when Lucius Cornelius Sulla, while proconsul in Cilicia, met the Parthian ambassador Orobazus. Plutarch reports that he managed to take the central seat between the Parthian Ambassador and an ambassador from Pontus, and concluded a treaty that set the Euphrates as the boundary between the two powers. Orobazus was executed on his return to Parthia for allowing Sulla to outmaneuver him, and Sulla himself later came under criticism for being too high-handed in his treatment of such a powerful nation. The first time the Romans came into direct military contact with Parthia came when Lucullus invaded Armenia in 69 BC, leading to diplomatic friction and clashes on the frontier between Armenia and Parthia. Over the following decades both empires became entangled in each other's civil wars, perhaps beginning with Crassus’s disastrous invasion of Parthia. Parthia was later involved in the civil war after the assassination of Julius Caesar. In 42 BC, when Antony placed a legion in Syria, Cassius’ envoy Labienus joined forces with king Orodes of Parthia and, led by Pacorus, attacked the Levant and the Asia Minor. However, this was not to last as Antony successfully sent his general Publius Ventidius Bassus to recover the lost territory. After some difficulty dealing with local Parthian appointee kings, the Romans finally subdued the regained province and installed Herod the Great as king. Antony’s forces attempted a crossing of the Euphrates at the city of Zeugma but were held back by Parthian defences and had to settle for annexing the Armenian kingdom after deposing its king. Relations during the Julio-Claudian dynasty Augustus was loath to seek further conflict with Parthia. However, the coveted standards were still held by the Parthians and this was of great concern to Augustus, forcing him to regain them through a less conventional method. Augustus set