Cilicia, convened with the Parthian diplomat Orobazus at the Euphrates river. The two agreed that the river would serve as the border between Parthia and Rome, although several historians have argued that Sulla only had authority to communicate these terms back to Rome. Despite this agreement, in 93 or 92 BC Parthia fought a war in Syria against the tribal leader Laodice and her Seleucid ally Antiochus X Eusebes (r. 95–92? BC), killing the latter. When one of the last Seleucid monarchs, Demetrius III Eucaerus, attempted to besiege Beroea (modern Aleppo), Parthia sent military aid to the inhabitants and Demetrius was defeated. Following the rule of Mithridates II, his son Gotarzes I succeeded him. He reigned during a period coined in scholarship as the "Parthian Dark Age," due to the lack of clear information on the events of this period in the empire, except a series of, apparently overlapping, reigns. It is only with the beginning of the reign of Orodes II in , that the line of Parthian rulers can again be reliably traced. This system of split monarchy weakened Parthia, allowing Tigranes II of Armenia to annex Parthian territory in western Mesopotamia. This land would not be restored to Parthia until the reign of Sinatruces (r. c. 78–69 BC). Following the outbreak of the Third Mithridatic War, Mithridates VI of Pontus (r. 119–63 BC), an ally of Tigranes II of Armenia, requested aid from Parthia against Rome, but Sinatruces refused help. When the Roman commander Lucullus marched against the Armenian capital Tigranocerta in 69 BC, Mithridates VI and Tigranes II requested the aid of Phraates III (r. c. 71–58). Phraates did not send aid to either, and after the fall of Tigranocerta he reaffirmed with Lucullus the Euphrates as the boundary between Parthia and Rome. Tigranes the Younger, son of Tigranes II of Armenia, failed to usurp the Armenian throne from his father. He fled to Phraates III and convinced him to march against Armenia's new capital at Artaxarta. When this siege failed, Tigranes the Younger once again fled, this time to the Roman commander Pompey. He promised Pompey that he would act as a guide through Armenia, but, when Tigranes II submitted to Rome as a client king, Tigranes the Younger was brought to Rome as a hostage. Phraates demanded Pompey return Tigranes the Younger to him, but Pompey refused. In retaliation, Phraates launched an invasion into