Numidia (202 BC – 46 BC) was an ancient Berber kingdom in present-day Algeria and part of Tunisia (North Africa) that later alternated between being a Roman province and being a Roman client state, and is no longer in existence today. It was located on the eastern border of modern Algeria, bordered by the Roman province of Mauretania (modern day Algeria) to the west, the Roman province of Africa (modern day Tunisia) to the east, the Mediterranean Sea to the north, and the Sahara Desert to the south. Its people were the Numidians.
During the first part of the Second Punic War, the eastern Massyli under their king Gala were allied with Carthage, while the western Massaesyli under king Syphax were allied with Rome. However in 206 BC, the new king of the eastern Massyli Massinissa allied himself with Rome, and Syphax of the Massaesyli switched his allegiance to the Carthaginian side. At the end of the war the victorious Romans gave all of Numidia to Massinissa of the Massyli. At the time of his death in 148 BC, Massinissa's territory extended from Mauretania to the boundary of the Carthaginian territory, and also southeast as far as Cyrenaica, so that Numidia entirely surrounded Carthage (Appian, Punica, 106) except towards the sea.
After the death of Massinisa he was succeeded by his son Micipsa. When Micipsa died in 118, he was succeeded jointly by his two sons Hiempsal I and Adherbal and Massinisa's illegitimate grandson, Jugurtha, of Berber origin who was very popular among the Numidians. Hiempsal and Jugurtha quarrelled immediately after the death of Micipsa. Jugurtha had Hiempsal killed, which led to open war with Adherbal.
After Jugurtha defeated him in open battle, Adherbal fled to Rome for help. The Roman officials, allegedly due to bribes but perhaps more likely because of a desire to quickly end conflict in a profitable client kingdom, settled the fight by dividing Numidia into two parts. Jugurtha was assigned the western half. (Later Roman propaganda claimed that this half was also richer, but in truth it was both less populated and developed.)
By 112 Jugurtha resumed his war with Adherbal. He incurred the wrath of Rome in the process, by killing some Roman businessmen who were aiding Adherbal. After a brief war with Rome, Jugurtha surrendered and received a highly favourable peace treaty, which raised suspicions of bribery once more. The local Roman commander was summoned to Rome to face corruption charges brought by his political rival Gaius Memmius. Jugurtha was also forced to come to Rome to testify against the Roman commander, where he was completely discredited once his violent and ruthless past became widely known, and after he had been suspected of murdering a Numidian rival.
War broke out between Numidia and the Roman Republic and several legions were dispatched to North Africa under the command of the Consul Quintus Caecilius Metellus. The war dragged out into a long and seemingly endless campaign as the Romans tried to inflict a decisive defeat on Jugurtha. Frustrated at the apparent lack of action, Metellus' lieutenant Gaius Marius returned to Rome to seek election as Consul. Successfully elected, Marius returned to Numidia to take control of the war. He sent his Quaestor Lucius Cornelius Sulla to neighbouring Mauretania in order to eliminate their support for Jugurtha. With the help of Bocchus I of Mauretania, Sulla was able to capture Jugurtha and bring the war to a conclusive end. Jugurtha was brought to Rome in chains and was placed in the Tullianum.
Jugurtha was executed by the Romans in 104 BC, after being paraded through the streets in Gaius Marius' Triumph.
Soon afterwards, in 25 BC, Juba was transferred to the throne of Mauretania, and Numidia was divided between Mauretania and the province of Africa Nova. Under Septimus Severus (193 AD), Numidia was separated from Africa Vetus, and governed by an imperial procurator; finally, under the new organization of the empire by Diocletian, Numidia was divided in two provinces: the north became Numidia Cirtensis, with capital at Cirta, while the south, which included the Aurès Mountains and was threatened by raids, became Numidia Militiana, "Military Numidia", with capital at the legionary base of Lambaesis. Subsequently however, Emperor Constantine the Great reunited the two provinces in a single one, administered from Cirta, which was now renamed to Constantina (modern Constantine, Algeria) in his honour. Its governor was raised to the rank of consularis in 320, and the province remained one of the seven provinces of the diocese of Africa until the invasion of the Vandals in 428 AD, which began its slow decay, accompanied by desertification. The province was retained under Vandal rule, but was effectively limited to the coastal areas by Berber raids. It was once again reestablished to Roman rule after the Vandalic War, when it became part of the new praetorian prefecture of Africa.
Lambaesis was the seat of the Legio III Augusta, and the most important strategic centre, as commanding the passes of the Mons Aurasius, a mountain block which separated Numidia from the Gaetulian tribes of the desert, and which was gradually occupied in its whole extent by the Romans under the Empire. Including these towns there were altogether twenty which are known to have received at one time or another the title and status of Roman colonies; and in the 5th century the Notitia Dignitatum enumerates no less than 123 sees whose bishops assembled at Carthage in 479.