The Batavians served with fidelity and distinction in all parts of the empire, and from the days of Augustus onwards formed a considerable part of the Praetorian guard.
His father was Flavius Manlius Boetius, and it is probable that the Flavius Boetius, the praetorian prefect who was put to death in A.D.
Rivalry had already existed between Stilicho and Rufinus, the praetorian praefect of the East, who had exercised considerable influence over the emperor and who now was invested with the guardianship of Arcadius.
On his father's death in 85 or 86 he was placed under the guardianship of two fellowcountrymen, his kinsman Ulpius Trajanus (afterwards the emperor Trajan), and Caelius Attianus (afterwards prefect of the praetorian guard).
The prefect of the praetorian guard was now the most important person in the state next to the emperor, and subsequently became a supreme judge of appeal.