 Complete the following phrase:  The Romans fought a prolonged and indecisive campaign in the East against the Parthians beginning in 53 BC, commencing with the defeat of Marcus Licinius Crassus close benefactor of Julius Caesar and his 35,000 legionaries at Carrhae. This initially unexpected and humiliating defeat for Rome was followed by numerous campaigns over the next two centuries entailing many notable engagements such as: the Battle of Cilician Gates, Mount Gindarus, Mark Antonys Parthian Campaign and finally culminating in the bloody Battle of Nisibis in 217 AD, which resulted in a slight Parthian victory, and Emperor Macrinus being forced to concede peace with Parthia. As a result of this lingering period of exposure to cataphracts, by the 4th century, the Roman Empire had adopted a number of vexillations of mercenary cataphract cavalry see the Notitia Dignitatum, such as the Sarmatian Auxiliaries. The Romans deployed both native and mercenary units of cataphracts throughout the Empire, from Asia Minor all the way to Britain, where a contingent of 5,500 Sarmatians including cataphracts, infantry, and non-combatants were posted in the 2nd century by Emperor Marcus Aurelius see 