Egypt was formed into a separate diocese in about 381. According to the
Notitia Dignitatum, which for the Eastern part of the Empire dates to ca. 401, the diocese came under a
vicarius of the
praetorian prefecture of the East, with the title of
praefectus augustalis, and included six provinces: •
Aegyptus (western Nile delta), originally established in the early 4th century as
Aegyptus Iovia, under a
praeses •
Augustamnica (eastern Nile delta), originally established in the early 4th century as
Aegyptus Herculia, under a
corrector •
Arcadia (central), established ca. 397 and having previously briefly listed in the 320s as
Aegyptus Mercuria, under a
praeses •
Thebais (southern), under a
praeses •
Libya Inferior or
Libya Sicca, under a
praeses •
Libya Superior or
Pentapolis, under a
praeses Parallel to the civil administration, the Roman army in Egypt had been placed under a single general and military governor styled
dux (
dux Aegypti et Thebaidos utrarumque Libyarum) in the
Tetrarchy. Shortly after the creation of Egypt as a separate diocese (between 384 and 391), the post evolved into the
comes limitis Aegypti, who was directly responsible for
Lower Egypt, while the subordinate
dux Thebaidis was in charge of Upper Egypt (Thebais). In the middle of the 5th century, however, the latter was also promoted to the rank of
comes (
comes Thebaici limitis). The two officers were responsible for the
limitanei (border garrison) troops stationed in the province, while until the time of
Anastasius I the
comitatenses field army came under the command of the
magister militum per Orientem, and the
palatini (guards) under the two
magistri militum praesentales in
Constantinople. The
comes limitis Aegypti enjoyed great power and influence in the diocese, rivalling that of the
praefectus augustalis himself. From the 5th century, the
comes is attested as exercising some civilian duties as well, and from 470 on, the offices of
comes and
praefectus augustalis were sometimes combined in a single person. This tendency to unite civil and military authority was formalized by
Justinian I in his 539 reform of Egyptian administration. The diocese was effectively abolished, and regional ducats established, where the presiding
dux et augustalis was placed above the combined civil and military authority: •
dux et augustalis Aegypti, controlling
Aegyptus I and
Aegyptus II •
dux et augustalis Thebaidis, controlling
Thebais superior and
Thebais inferior •
Augustamnica I and
Augustamnica II were likewise probably — the relevant portion of the edict is defective — were placed under a single
dux et augustalis • in the two Libyan provinces, the civil governors were subordinated to the respective
dux •
Arcadia remained under its
praeses, probably subordinated to the
dux et augustalis Thebaidos, and a
dux et augustalis Arcadiae does not appear until after the
Persian occupation of 619–629. ==
Praefecti Augustalii of the Diocese ==