Typical Parthian soldiers during the 1st Century. They relied on armies made up of highly mobile cavalry archers to harass the enemy and draw them out of their formation and heavily armored cataphracts to run them down in the open. These forces were able to defeat much larger Roman armies by slowly wearing them down over the course of days or even weeks by attacking isolated groups of enemies then retreating before the enemy can respond. These tactics are how the Parthians massacred Crassus and forced Mark Anthony to retreat after suffering great losses. The Parthians did not have very sophisticated siege techniques unlike the later Sassanids. The ability for the smaller Parthian armies to slowly wear Roman armies down without ever giving them the chance for a decisive engagement can explain why Rome was never able to conquer Parthia and the inability of these ultra mobile units to defeat defending armies and take cities can explain why Parthia was never able to conquer much Roman territory, thus contributing to the relatively static borders that developed between the two empires.