Originally, in ancient Rome, this office was equivalent to the later English "vice-" (as in "deputy"), used as part of the title of various officials.
[1] Later, in the 290s, Emperor Diocletian carried out a series of administrative reforms, ushering in the period of the Dominate.
These reforms also saw the number of Roman provinces increased, and the creation of a new administrative level, the diocese.
The dioceses were headed by a vicarius, or, more properly, by a vices agens praefecti praetorio ("deputy of the praetorian prefect").
[2] According to the Notitia dignitatum (an early 5th century imperial chancery document), the vicarius had the rank of vir spectabilis; the staff of a vicarius, his officium, was rather similar to a gubernatorial officium.