The city was founded by and named after one of the rulers of the Ptolemaic Kingdom, probably Ptolemy III Euergetes (246–221 BC).
What had been a small Greek settlement of unknown name that originated in the late 7th century BC and that acted as a port for the city of Barca, 24 kilometres (15 mi) inland, he transformed into a city that enclosed 280 hectares within its walls.
Ptolemais probably served as the residence of the Ptolemaic governor of the region but, in spite of its large area, its population did not rival that of Cyrene, which under Roman rule became the capital of the region that, from then on, and still today, is called Cyrenaica.
However, the term "Pentapolis" also continued to be used.

Ptolemais became a Roman possession in 96 BC.
It was soon included in the Roman province of Crete and Cyrenaica.
With Diocletian's alteration of the administrative structure, Ptolemais became the capital of the province of Libya Superior or Libya Pentapolis.
It later decayed and was replaced as capital of the province by Apollonia.

The 365 Crete earthquake struck the region and destroyed all the five major cities of the Pentapolis.
Ptolemais survived the tragedy in relatively good condition.
It served as capital of Cyrenaica until 428.
The city was destroyed by the Libyans in 411.
During the reign of Justinian I the city was rebuilt, but it never regained its powers and was again destroyed during the Muslim conquest of the Maghreb in the 7th century.
The city was founded by and named after one of the rulers of the Ptolemaic Kingdom, probably Ptolemy III Euergetes (246–221 BC). What had been a small Greek settlement of unknown name that originated in the late 7th century BC and that acted as a port for the city of Barca, 24 kilometres (15 mi) inland, he transformed into a city that enclosed 280 hectares within its walls. Ptolemais probably served as the residence of the Ptolemaic governor of the region but, in spite of its large area, its population did not rival that of Cyrene, which under Roman rule became the capital of the region that, from then on, and still today, is called Cyrenaica. However, the term "Pentapolis" also continued to be used.
Ptolemais became a Roman possession in 96 BC. It was soon included in the Roman province of Crete and Cyrenaica. With Diocletian's alteration of the administrative structure, Ptolemais became the capital of the province of Libya Superior or Libya Pentapolis. It later decayed and was replaced as capital of the province by Apollonia.
The 365 Crete earthquake struck the region and destroyed all the five major cities of the Pentapolis. Ptolemais survived the tragedy in relatively good condition. It served as capital of Cyrenaica until 428. The city was destroyed by the Libyans in 411. During the reign of Justinian I the city was rebuilt, but it never regained its powers and was again destroyed during the Muslim conquest of the Maghreb in the 7th century.
Ptolemais, Cyrenaica