In its earliest days it was probably a port of call on the Phoenician trade routes across the region, and by the 6th century BC was administered from Carthage.

A small port developed at the mouth of the wadi, which grew in size when the city became part of the Roman Empire under the Emperor Trajan in 111 BC. Under the patronage of the Roman Emperor Septimus Severus (AD193-211), who was born in Leptis Magna, the city flourished and gradually spread inland and in a westerly direction along the coast. Many of the major buildings date from this period, and the population at this time was about 70,000.