kinsmen and magi, two groups from which "the kings were appointed." Of the great noble Parthian families listed at the beginning of the Sassanian period, only two are explicitly mentioned in earlier Parthian documents: the House of Suren and the House of Karen. The historian Plutarch noted that members of the Suren family, the first among the nobility, were given the privilege of crowning each new Arsacid King of Kings during their coronations. Military The Parthian Empire had no standing army, yet were able to quickly recruit troops in the event of local crises. There was a permanent armed guard attached to the person of the king, comprising nobles, serfs and mercenaries, but this royal retinue was small. Garrisons were also permanently maintained at border forts; Parthian inscriptions reveal some of the military titles granted to the commanders of these locations. Military forces could also be used in diplomatic gestures. For example, when Chinese envoys visited Parthia in the late 2nd century BC, the Shiji maintains that 20,000 horsemen were sent to the eastern borders to serve as escorts for the embassy, although this figure is perhaps an exaggeration. The main striking force of the Parthian army was its cataphracts, heavy cavalry with man and horse decked in mailed armor. The cataphracts were equipped with a lance for charging into enemy lines, but were not equipped with bows and arrows which were restricted to horse archers. Due to the cost of their equipment and armor, cataphracts were recruited from among the aristocratic class who, in return for their services, demanded a measure of autonomy at the local level from the Arsacid kings. The light cavalry was recruited from among the commoner class and acted as horse archers; they wore a simple tunic and trousers into battle. They used composite bows and were able to shoot at enemies while riding and facing away from them; this technique, known as the Parthian shot, was a highly effective tactic. The heavy and light cavalry of Parthia proved to be a decisive factor in the Battle of Carrhae where a Parthian force defeated a much larger Roman army under Crassus. Light infantry units, composed of levied commoners and mercenaries, were used to disperse enemy troops after cavalry charges. The size of the Parthian army is unknown, as is the size of the empire's overall population. However, archaeological excavations in former Parthian urban centers reveal