Conflicts against Athanaric
Socrates Scholasticus, Sozomen, and Zosimus refer to conflicts between Fritigern and Athanaric. Ammianus Marcellinus and Philostorgius do not record such conflicts.
According to Socrates, Fritigern and Athanaric were rival leaders of the (Therving) Goths. As this rivalry grew into warfare, Athanaric gained the advantage, and Fritigern asked for Roman aid. The Emperor Valens and the Thracian field army intervened, Valens and Fritigern defeated Athanaric, and Fritigern converted to Christianity, following the same teachings as Valens followed. Sozomen follows Socrates' account.
According to Zosimus, Athanaric (Athomaricus) was the king of the Goths (Scythians). Sometime after their victory at Adrianople, and after the accession of Theodosius, Fritigern, Alatheus, and Saphrax moved north of the Danube and defeated Athanaric, before returning south of the Danube.
The earliest sources that mention Fritigern originate from the period in which Valens, emperor of the Roman Empire, attacked the Thervingi (367-369) and from the period in which the Huns raided the Thervingi (ca. 376). In this period a civil war may have broken out between Fritigern and Athanaric, a prominent Therving ruler. Before or during this civil war, Fritigern converted to ("Arian") Christianity. Nevertheless, Athanaric seems to have won this war. Athanaric later led the Thervingi in battle against the Huns in 376.