Under the Roman Republic and Empire, Numidia was a part of Africa north of the Sahara, the boundaries of which at times corresponded roughly with those of modern Algeria. Its earliest inhabitants were divided into tribes and clans and were racially indistinguishable from the other Berber inhabitants of early North Africa. From the 6th century BC points along the coast were occupied by the Carthaginians, who by the 3rd century BC had expanded into the interior as far as Theveste (Tébessa). Numidians were frequently found in the Carthaginian armies by that time.

The inhabitants remained seminomadic, however, until the reign of Masinissa, the chief of the Massyli tribe living near Cirta (Constantine). During the Second Punic War he was initially an ally of Carthage, but he went over to the Roman side in 206 BC and was given further territory extending as far as the Mulucha (Moulouya) River. For nearly 50 years Masinissa retained the support of Rome as he tried to turn the Numidian pastoralists into peasant farmers. He also seized much Carthaginian territory and probably hoped to rule all of North Africa.