History of the Roman Empire
Theodosius was the last Emperor who ruled over the whole Empire. After his death in 395, he gave the two halves of the Empire to his two sons Arcadius and Honorius; Arcadius became ruler in the East, with his capital in Constantinople, and Honorius became ruler in the West, with his capital in Milan and later Ravenna. The Roman state would continue to have two different emperors with different seats of power throughout the 5th century, though the Eastern Romans considered themselves to be the only ones who were fully Roman. Latin was used in official writings as much as, if not more than, Greek and the two halves were nominally, culturally and historically, if not politically, the same state.
Theodosian dynasty
Its founding father was Flavius Theodosius (often referred to as Count Theodosius), a great general who had saved Britannia from the Great Conspiracy. His son, Flavius Theodosius was made emperor of the Eastern Roman Empire in 379, and briefly reunited the Roman Empire 394–395 by defeating the usurper Eugenius. Theodosius I was succeeded by his sons Honorius in the West and Arcadius in the East. The House of Theodosius was related to the Valentinian Dynasty by marriage, since Theodosius I had married Galla, a daughter of Valentinian I. Their daughter was Galla Placidia. The last emperor in the West belonging to the dynasty was Galla Placidia's son Valentinian III. The last emperor of the dynasty in the East was Theodosius II, the son of Arcadius. Later, both in the East and in the West, the dynasty briefly continued, but only through marriages: Marcian became emperor by marrying Pulcheria, the older sister of Theodosius II, after the death of the latter, Petronius Maximus was married to Licinia Eudoxia, the daughter of Theodosius II, and Olybrius was married to Placidia, the daughter of Valentinian III. Anthemius is also sometimes counted to the dynasty as he became a son-in-law of Marcian. Descendants of the dynasty continued to be part of the East Roman nobility at Constantinople until the end of the 6th century.In "italics" the Augusti and the Augustae.