Aksum was the kingdom of the northern Ethiopian highlands, a trading power connected to the Red Sea and beyond, and it adopted Christianity in the fourth century under King Ezana, which places it among the earliest states anywhere to do so.
The conversion is unusually well evidenced by the standards of the period, because Ezana left inscriptions in Ge'ez, Sabaean and Greek, and the religious language in them changes. Earlier texts invoke the gods of the traditional pantheon; later ones invoke the Lord of Heaven and Earth in monotheist terms without naming the older gods. His coinage changes at the same point, replacing a disc and crescent with a cross, which makes Aksumite coins one of the clearest numismatic records of a state conversion in existence.
The church that resulted was tied to Alexandria: its head was a bishop appointed by the Coptic patriarch of Egypt, an arrangement that lasted until 1959. It followed the Alexandrian christology and therefore stood outside the Chalcedonian settlement of 451 along with the Coptic, Syriac and Armenian churches.
The kingdom declined from the seventh century as trade routes shifted, and the Christian centre moved south into the highlands, where later dynasties built the rock-hewn churches of Lalibela and a monastic tradition that has continued without interruption. Ge'ez remains the liturgical language.