Nazianzus (Greek: Ναζιανζός, Nazianzos) was a small town in the late Roman province of Cappadocia Tertia.
Its history in antiquity is unknown. It became the Turkish village of Nenizi east of Ak-Serai (formerly Archelais), in the Ottoman villayet of Koniah, but has sometimes been wrongly identified with Diocaesarea.
At the beginning of the 4th century Nazianzus was suffragan to Caesarea Mazaca; under Emperor Valens it formed part of Cappadocia Secunda, the metropolis of which was Tyana. Later it became part of Cappadocia Tertia and depended on its Metropolitan of Mocessus. Finally it became a metropolitan see itself under Diogenes.
In 1370 it was united to the metropolitan see of Caesarea Mazaca (modern Kayseri).
Up to the year 1200, fourteen of its bishops are known. Its name is inseparably connected with its illustrious doctor and poet-bishop, St. Gregory of Nazianzus, who became bishop of Constantinople and Doctor of the Church. His father Gregory of Nazianzus the Elder had been a member of a Jewish-pagan sect called the Hypsistarians but was converted to Christianity and became Bishop of Nazianzus.