The three earliest appointments Blassianus received, which comprise the steps of the tres militiae that equites followed in their military career, are recorded in several inscriptions from Trieste.
Anthony Birley notes that "it would fit the chronology of his career if he obtained a commission from A. Platorius Nepos, governor of Britain 122-4, who was patron of Aquileia, a city close to Blassianus' home".
[2] The remainder of his career in the imperial service is documented in a fragmentary inscription recovered from Ostia Antica honoring him as prefect by the collegium fabrum tignariorum.
First was praefectus vigilum, commander of the vigiles or nightwatch of Rome; he may have preceded Gaius Tettius Maximus in this post.
Next was an appointment as praefectus annonae; which may have fallen between the tenures of Lucius Volusius Maecianus and Titus Furius Victorinus.