Cyrenaica, historic region of North Africa and until 1963 a province of the United Kingdom of Libya. As early as c. 631 bc Greek colonists settled the northern half of ancient Cyrenaica, known then as Pentapolis for the five major cities they established: Euhesperides (Banghāzī), Barce (al-Marj), Cyrene (Shaḥḥāt), Apollonia (Marsa Sūsah), and Tenchira (Tūkrah). In later times Ptolemais (Ṭulmaythah) and Daims-Zarine (Darnah) also rose to prominence.
Under the Ptolemies of Egypt (ruled 323–30 bc), the inland cities of Barce and Cyrene declined and commercial competition with Egypt and Carthage intensified. Cyrenaica itself became a Roman province in combination with Crete in 67 bc. After Arab armies under the leadership of ʿAmr ibn al-ʿĀṣ had conquered the country in 642, inland Cyrenaica regained importance, lying as it did on the direct route between Alexandria and al-Qayrawān, and Barce became its chief centre. Ruled by a succession of Egyptian-based dynasties in the later Middle Ages, Cyrenaica came under the nominal suzerainty of the Ottoman Empire after the 15th century; in the mid-19th century the region became the centre of the Sanūsīyah religious brotherhood and dynasty.
As a result of the Italo-Turkish War (1911–12), Cyrenaica, with Tripolitania, was ceded to Italy in 1912, and by 1940 about 50,000 Italian peasant colonists were converting northern Cyrenaica into the semblance of an Italian province, cultivating cereals, vines, and fruit trees. In 1939, along with Fezzan and Tripolitania, Cyrenaica was incorporated into the kingdom of Italy.
Cyrenaica became a major theatre of operations during World War II. When the British finally occupied the area after the victory at el-Alamein in Egypt (al-ʿAlamayn; October 1942), the Italian colonists were evacuated, and the population was once again 98 percent Muslim and Arabic-speaking.
After World War II the inability of the great powers to agree on the future of the former Italian colonies protracted the British military administration, and a united kingdom of Libya comprising the three provinces was not proclaimed until 1951. In 1963 the provinces were abolished and the country became a unitary state.