Valentinian I is proclaimed Roman Emperor.

Valentinian I, sometimes known as Valentinian the Great, was Roman emperor from 364 to 375. He ruled the Western half of the empire, while his brother Valens ruled the East. During his reign, he fought successfully against the Alamanni, Quadi, and Sarmatians, strengthening the border fortifications and conducting campaigns across the Rhine and Danube. Also, his general Theodosius the Elder defeated a revolt in Africa and the Great Conspiracy. Valentinian founded the Valentinian dynasty, with his sons Gratian and Valentinian II succeeding him in the western half of the empire and his daughter Galla marrying emperor Theodosius I.

The Roman emperor was the ruler and monarchical head of state of the Roman Empire, starting with the granting of the title augustus to Octavian in 27 BC. The term emperor is a modern convention, and did not exist as such during the Empire. When a given Roman is described as becoming emperor in English, it generally reflects his accession as augustus, and later as basileus. Another title used was imperator, originally a military honorific, and caesar, originally a cognomen. Early emperors also used the title princeps alongside other Republican titles, notably consul and pontifex maximus.

February 26 is the 57th day of the year in the Gregorian calendar; 308 days remain until the end of the year.