Apollonia (Greek: Απολλωνία) in Cyrenaica (modern Libya) was founded by Greek colonists and became a significant commercial centre in the southern Mediterranean. It served as the harbour of Cyrene, 20 km (12 mi) to the southwest. The Greek geographer and mathematician Eratosthenes was born there.

Apollonia was one of the five towns of the Libyan Pentapolis. The early foundation levels of the city of Apollonia are below sea level due to submergence in earthquakes, while the upper strata of the latest Byzantine Christian periods are several meters above sea level, built upon the accumulated deposits of previous periods. The existence of buildings in the sea was noted by Beechey (1827), with some rough drawings. The main archaeological sources on land are Goodchild for publications in the 1950’s, and Laronde more recently. In 1958 and 1959 Nicholas Flemming, then an undergraduate at Cambridge University, led teams of undergraduates trained in scuba diving and underwater surveying to map the large sector of the city beneath the sea. The results of this work were published, complete with maps and diagrams of underwater buildings in the references cited below. Carlo Beltrame and colleagues have recently made an underwater photographic survey of some of the buildings.

Cyrenaica ( /saɪrɨˈneɪ.ɨkə/ SY-rə-NAY-ə-kə; Ancient Greek: Κυρηναϊκή, after the city of Cyrene; Arabic: برقة‎ Barqah; Berber: Berqa) is the historical name of the eastern region in Libya, which self-declared autonomy. In a tribal meeting the National Federal Bloc party declared Cyrenaica as self-autonomous region, but no actual authority has been observed on the ground, as the National Transitional Council still the defacto authority in all of Libya. Also known as Pentapolis in antiquity, it was part of the Creta et Cyrenaica province during the Roman period, later divided in Libia Pentapolis and Libia Sicca. During the Islamic period, the area came to be known as Barqa, after the city of Barca.

Cyrenaica was the name of an administrative division of Italian Libya from 1927 through 1943, then under British military and civil administration from 1943 through 1951, and finally in the Kingdom of Libya from 1951 through 1963. In a wider sense, which is still used, Cyrenaica is composed of all of the eastern part of Libya, including the Kufra District. Cyrenaica is adjacent to Tripolitania in the northwest and Fezzan in the southwest. The region that used to be Cyrenaica officially through 1963 is now divided up into several shabiyat, the administrative divisions of Libya.