Vicarius is a Latin word, meaning substitute or deputy. It is the root and origin of the English word "
vicar." Originally, in ancient Rome, this was an equivalent to the English "
vice-" (as in "deputy"), used as part of the title of various officials. Each vicarius was assigned to a specific superior official, after whom his full title was generally completed by a
genitive (e.g. Vicarius Praetoris). Later, during the period of the
Roman Empire known as the
Dominate, a vicarius was the imperial deputy responsible for the lawfulness of a group of
Roman provinces called a
diocese. The title was used without a genitive, simply as "vicarius". This position was introduced under Emperor
Diocletian who reformed the Roman Empire, collegially, into the
Tetrarchy. Among other changes, the eastern and western empires were each divided into two large
praetorian prefectures. Each of the four prefectures was run by a
Praetorian Prefect and contained several subdivisions known as dioceses, which in turn were divided into provinces. The vicarius was the governor of a diocese, and was responsible for a number of provinces, each province with its own
governor. The various prefectures, dioceses and provinces are listed systematically in their hierarchical groupings in the article
Roman province.
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