Surena, whose achievements had made him too dangerous, was killed by Orodes, and Pacorus I, the son and heir of the king was defeated by Cassius in 51 BC.

[7] During his father's reign, Orodes seemingly enjoyed close connections with the eastern part of the Parthian realm, specifically with the House of Suren, and possibly also with the Indo-Scythians.

The Roman proconsul marched with Mithridates IV to the Euphrates, but turned back to restore another ruler, Ptolemy XII Auletes of Egypt, to his throne.

[14] Around the same time, Marcus Licinius Crassus, one of the Roman triumvirs, who was now proconsul of Syria, had been preparing to invade the Parthian realm in belated support of Mithridates IV.

[18] As Crassus' army marched to Carrhae (modern Harran, southeastern Turkey), Orodes invaded Armenia, cutting off support from Artavasdes.

[22] Surena's 1,000 cataphracts (armed with lances) and 9,000 horse archers were outnumbered roughly four to one by Crassus' army, comprising seven Roman legions and auxiliaries including mounted Gauls and light infantry.

[23] The horse archers employed the "Parthian shot" tactic: feigning retreat to draw enemy out, then turning and shooting at them when exposed.

[26] After his death, the Parthians allegedly poured molten gold down his throat, in a symbolic gesture mocking Crassus' renowned greed.

[31] With his camp followers, war captives, and precious Roman booty, Surena traveled some 700 km (430 mi) back to Seleucia, where his victory was celebrated.

[33] Orodes sided with Pompey in the civil war against Julius Caesar and even sent troops to support the anti-Caesarian forces at the Battle of Philippi in 42 BC.

[34] Quintus Labienus, a general loyal to Cassius and Brutus, sided with Parthia against the Second Triumvirate in 40 BC; the following year he invaded Syria alongside Pacorus I.

[35] The triumvir Mark Antony was unable to lead the Roman defense against Parthia due to his departure to Italy, where he amassed his forces to confront his rival Octavian and eventually conducted negotiations with him at Brundisium.

Publius Ventidius Bassus, an officer under Mark Antony, defeated and then executed Labienus at the Battle of the Cilician Gates (in modern Mersin Province, Turkey) in 39 BC.

[38] Shortly afterward, a Parthian force in Syria led by general Pharnapates was defeated by Ventidius at the Battle of Amanus Pass.

[40] Fearing that his position might become endangered, Phraates IV executed all his half-brothers–the sons of Orodes and Laodice, partially due to their maternal descent being greater than that of his own.

[43][44] In the Parthian era, Iranians used Hellenistic iconography to portray their divine figures,[46][47] thus the investiture scene can be associated with the Avestan khvarenah, i.e. kingly glory.

[44][48] According to the modern historian Khodadad Rezakhani, the introduction of this new portrayal may have been due to the enlargement of Orodes' authority after the Battle of Carrhae in 53 BC.

[43] Under Orodes and his son Phraates IV, the production of coins reached its zenith, with the only Parthian ruler having similar numbers being Mithridates II (r. 124–88 BC).