The city appears to have been founded by Phoenician colonists sometime around 1100 BC, although it didn't 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.
It remained as such until the reign of the Roman emperor Tiberius, when Leptis Magna 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-imporant city in Africa, rivaling Carthage and Alexandria. In 205, he and the imperial family visited the city and received great honors.
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. 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. But 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 10 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. By the time the Saracens overran Tripolitania in the 650s, the city was abandoned except for a Byzantine garrison force.
Today, the site of Leptis Magna is the site of some of the most impressive ruins of the Roman period.