Flavius Caesarius (floruit 386-403) was a politician of the Eastern Roman Empire, who served under Emperors Theodosius I and Arcadius. Caesarius was magister officiorum (386-387),praetorian prefect of the East (395-397 and 400-403) and consul in 397.
Caesarius was the son of the Consul of 361, Taurus, and the elder brother of Aurelianus, with whom he contended for power. His devotion to his wife is noted by Sozomen.
In 386 he is attested as magister officiorum. As such, he was sent by Emperor Theodosius I to Antioch in 387, where the population had revolted against taxation. Caesarius, together with Ellobicus, then magister militum per Orientem, held an inquiry. Caesarius paid particular attention for the situation of the citizens of Antioch and in his report to the Emperor pleaded for clemency for them. The Antiochian orator Libanius thanked him in an oration for this.
Despite his merits, Caesarius was not appointed to higher offices in the following years, when Rufinus was in power as magister officiorum and praetorian prefect of the East. It has been suggested that Caesarius, despite being Orthodox, was not strict enough against heretics. Meanwhile, his younger brother Aurelianus made career, succeeding Rufinus as magister officiorum in 392 and then holding the office of praefectus urbi of Constantinople between 393 and 394.
After Rufinus had been killed in November 395, Caesarius succeeded him as praetorian prefect of the East. As such, he nullified several laws Rufinus had passed, including a ban of Lycians from Constantinople - Rufinus's enemies, Eutolmius Tatianus and Proculus had been Lycians - and the prohibition against Arian Eunomians from making wills. However, Caesarius did not act out of opposition to Rufinus, as is shown by the fact that he also issued a law that allowed the widow of proscribed men from losing their properties (the widow of Rufinus probably benefited by this law).