The city Leptis Magna appears to have been founded by Phoenician colonists sometime around 1100 BC. The town did not achieve prominence until Carthage became a major power in the Mediterranean Sea in the 4th century BC. It nominally remained part of Carthage's dominions until the end of the Third Punic War in 146 BC and then became part of the Roman Republic, although from about 200 BC onward, it was for all intents and purposes an independent city.
Leptis Magna remained as such until the reign of the Roman emperor Tiberius, when the city and the surrounding area were formally incorporated into the empire as part of the province of Africa. It soon became one of the leading cities of Roman Africa and a major trading post. Leptis achieved its greatest prominence beginning in 193, when a native son, Lucius Septimius Severus, became emperor. He favored his hometown above all other provincial cities, and the buildings and wealth he lavished on it made Leptis Magna the third-most important city in Africa, rivaling Carthage and Alexandria. In 205, he and the imperial family visited the city and received great honors. Among the changes that Severus introduced were to create a magnificent new forum and to rebuild the docks. The natural harbour had a tendency to silt up, but the Severan changes made this worse, and the eastern wharves are extremely well preserved, since they were hardly used.
Leptis over-extended itself at this period. During the Crisis of the Third Century, when trade declined precipitously, Leptis Magna's importance also fell into a decline, and by the middle of the fourth century, large parts of the city had been abandoned. Ammianus Marcellinus recounts that the crisis was worsened by a corrupt Roman governor named Romanus during a major tribal raid who demanded bribes to protect the city. The ruined city could not pay these and complained to the emperor Valentianian. Romanus then bribed people at court and arranged for the Leptan envoys to be punished "for bringing false accusations". It enjoyed a minor renaissance beginning in the reign of the emperor Theodosius I.
In 439, Leptis Magna and the rest of the cities of Tripolitania fell under the control of the Vandals when their king, Gaiseric, captured Carthage from the Romans and made it his capital. Unfortunately for the future of Leptis Magna, Gaiseric ordered the city's walls demolished so as to dissuade its people from rebelling against Vandal rule. The people of Leptis and the Vandals both paid a heavy price for this in 523 when a group of Berber raiders sacked the city. Belisarius recaptured Leptis Magna in the name of Rome ten years later, and in 534, he destroyed the kingdom of the Vandals. Leptis became a provincial capital of the Eastern Roman Empire (see Byzantine Empire) but never recovered from the destruction wreaked upon it by the Berbers. It was the site of a massacre of Berber chiefs of the Leuathae tribal confederation by the Roman authorities in 543. By the time of the Arab conquest of Tripolitania in the 650s, the city was abandoned except for a Byzantine garrison force.1