The Tetrarchy of Judea was formed following the death of Herod the Great in 4 BC, when his kingdom was divided between his sons as an inheritance. It persisted into the first century, until the kingdom was re-united under Herod Agrippa I in 41AD.
At the time of his death Herod ruled over most of Palestine, and territories beyond the Jordan, as a client of the Roman Empire; after his death the kingdom was divided between three of his sons. Archelaus, his son by his fourth wife Malthace, received the lion's share of the kingdom; Idumaea, Judaea and Samaria, and the title of Ethnarch ("ruler of the people"; in this case, the Jews). Herod Antipas, Archelaus’ brother, became Tetrarch of Galilee and Perea. Philip, Herod’s son by his fifth wife Cleopatra of Jerusalem, became Tetrarch of the northern part of Herod’s kingdom. Luke the evangelist lists Philip’s territories as Iturea and Trachonitis: Josephus gives his territories variously as Batanea, Gaulanitis, Trachonitis and Paneas (Antiquities XVII, 8 : 1) and Batanea, Trachonitis, Auranitis, and “ a certain part of what is called the House of Zenodorus”(Ant XVII , 11 : 4). A number of these names refer to the same places; they are all to be found now in modern-day Syria and Lebanon.
In a turbulent period of history, the rule of the tetrarchs was relatively uneventful. The most trouble fell to Archelaus, who was faced with sedition by the Pharisees at the beginning of his reign, and crushed it with great severity. After ruling for 10 years he was removed by the emperor Augustus in 6 AD, following complaints about his cruelty and his offences against the Mosaic law. He was replaced by a Roman procurator, and his territory re-organized as the Roman province of Iudaea. Philip ruled Ituraea and Trachonitis until his death in 34 AD when he was succeeded as tetrarch by Herod Agrippa I, who had previously been ruler of Chalcis. Agrippa surrendered Chalcis to his brother Herod III and ruled in Philip’s stead. On the death of Herod Antipas in 39 AD Herod Agrippa became ruler of Galilee also, and in 41 AD, as a mark of favour by the emperor Claudius, succeeded the Roman prefect Marulus as ruler of Iudaea. With this acquisition, the kingdom of the Jews was re-established, and the Tetrarchy was at an end.
The word Tetrarch suggests four rulers (“ruler of a quarter “); however Josephus, in the context of describing Herod’s legacy, only mentions three. He refers to Archelaus, who had “one half of that which had been subject to Herod”, and for Philip and Antipas “the other half, divided into two parts”. (Antiquities XVII , 11 : 4) On the other hand, Luke the Evangelist refers to Lysanias, tetrarch of Abilene, in his list of rulers at the time of John the Baptist, alongside Pontius Pilate,(one of a series of Roman governors who replaced Archelaus), Herod (Antipas) and Philip.(Luke 3 : 1) Josephus’ reference to one half the kingdom may signify two quarters, that Archelaus was ruler of two tetrarchies. This would suggest that division into quarters was already established, and that Lysanias’ quarter was part of a different tetrarchy in Syria; this is credible, as Herod III, brother of Herod Agrippa I, was tetrarch of Chalcis, which was to the north, outside Herod’s kingdom. Or it may be that Josephus, in describing the inheritances of Herod’s sons, omitted to mention Lysanias, or his predecessor, as they were not Herodians. The reference to “one half of the kingdom” could then be understood as a geographical, rather than a political observation; Archelaus’ share of the kingdom covered about half the territory, and more than half the revenue, owned by Herod. It is the view of W Smith, referring to Abilene, that Abilene,or part of it, was subject to Herod before his death, and held by Lysanias as a tetrarchy from him. The territory was returned later to the Herodians, the first part by Caligula to Herod Agrippa I, the remainder by Claudius to Herod Agrippa II.