1. Hellenistic period

From the end of the 3^rd cent. BC onwards, Rome gradually began gaining access to the political arena of the eastern Mediterranean through diplomatic or military means. As a result, a number of Hellenistic kingdoms came under the direct influence of Rome and the power balance in the region started to change. When they were not in war with Rome, Alexander the Great’s successors forged alliances with Rome and remained on the throne upon the consent of Rome. Most characteristic is the example of the last king of Pergamon, Attalus, who bequeathed his kingdom to the Roman people in 133 BC. The relationships between Rome and the Hellenistic rulers were proven to be important for both parties and were maintained until Nero’s reign (54-68 AD), when the last kingdom was integrated into the provincial system of the imperial administration.

After Perseus’ defeat in Pydna in 168 BC, Rome became the dominant force in the Mediterranean and the kings who were well-disposed towards Rome were named its friends and allies (reges socii atque amici). These titles, mainly found in official treaties, were usually given to monarchs who had already assisted the Romans in the past and commited themselves to offering their services in the future. This alliance, however, was not mutual, since Rome rarely offered any kind of military aid. As a result, when a king accepted the title of friend and ally, he automatically accepted the role of the client king, whereas Rome played the role of the patron state. Almost all the vassal kings participated in the military operations of the Romans during the last two centuries of the Roman Republic (2^nd-1^st cent. BC) and accepted the title of friend and ally of Rome, which gave its bearers great prestige, especially when they exercised foreign policy.¹

In this context, Rome acknowledged the crowning of the new kings by granting them the title of rex, sending them the symbols of its power, especially the toga and the sceptre, and protecting them from potential usurpers of their throne. Thus, Rome was able to control the policy of its client kings or even dethrone those who did not meet its expectations, offering its protection to another member of the royal family.²

Although the monarchs were forbidden to sign peace treaties or forge alliances with peoples which were hostile to Rome, they were able, if they wished, to expand the boundaries of their kingdom through military means, on condition that they would not attack another friend or ally of the Roman people and that their interests would not conflict with the interests of their patron. Being in fide populi Romani, their main duty was the protection of their frontiers from raids of peoples or tribes who were hostile to Rome and the suppression of revolts within their dominion.³

Although Roman officials did not have the right to intervene in the internal affairs of the kingdoms without the consent of the senate (ius postliminii), kings, especially towards the end of the Roman Republic (1^st cent. BC), were answerable to the evocatio, according to which a Roman commander could ask for their military assistance. In many cases, Roman generals commanded foreign forces and kings commanded Roman auxiliary units (regia auxilia).⁴

The Hellenistic kingdoms were outside the boundaries of the imperium Romanum and their rulers were not subjected to control by Roman officials, enjoying the privileges of free cities (civitates liberae et foederatae). They were released from taxation although they were obliged to offer donations and valuable gifts to Roman generals, especially during the period of the civil wars of the 1^st cent. BC.⁵ However, they still had the right to choose their own successors and mint their own coinage. Theoretically speaking, they had the right to exert unlimited power within their dominions, rule their subjects similarly to their predecessors and implement their own laws. In reality, the interventions of the emperors in the internal affairs of the client kingdoms became more and more frequent from the end of the 1^st cent. BC onwards.⁶

2. Imperial period

After Octavian’s victory in Actium on 2 September 31 BC, no kingdom or city had the power to resist him apart from Egypt, Marcus Antonius' and Cleopatra’s seat. During his stay in Samos, from the end of the autumn of 31 BC to the first days of January 30 BC and the summer of the same year, Octavian received all the client kings and set the foundations for the organization of the eastern part of the Roman Empire.⁷

Although most of them had been enthroned by his adversary, Marcus Antonius, they retained their power upon Octavian’s approval and some of them expanded the boundaries of their dominions. As a token of their loyalty towards the Roman emperor, the rulers established new cities or renamed older ones, gining themthe names Caesarea or Sebaste after the emperor or Agrippias, Tiberias, etc. after members of the imperial house. They also built temples for the imperial cult and held games and festivals in honour of the imperial family.

Octavian took punitive measures against some of them not because of their alliance with Marcus Antonius in Actium – the first Roman emperor exercised an uncommonly moderate policy (clementia) towards his political opponents – but because of their administrative incompetency and their disbelief or hostility towards the institutions of Rome. A characteristic example which proves the importance Augustus attributed to the loyalty and administrative skills of the kings is the example of Herod of Judaea, known from the story of Christ’s birth. Upon meeting Augustus in 30 BC, he tried to present his alliance with Marcus Antonius as an act of friendship towards Rome. Augustus kept him on the throne and gave him the title of friend of the Caesar and friend of the Roman people because Herod was proven to be one of the most loyal friends of Rome, especially against the Parthians, and because he was capable of ruling the rather troublesome province of Judaea.⁸

3. Assessment

To sum up, Republican Rome and the first Roman emperors managed to make use of the structures of the last Hellenistic kingdoms, the anachronistic remains of a political organization which belonged to the past, to the advantage of the Roman Empire. Assisted by the client kings, Rome managed to confront the hostile raids more effectively and rule peoples who, due to social structures and religious beliefs, could not be directly integrated into its administrative system. From the beginning of the Imperial period onwards, the Roman military and administrative system was improved to such an extent that the assistance of the client kings was not deemed as necessary as during the Roman Republic and the institution was abolished.⁹