As a rule set by Augustus there were always 10 senatorial provinces in the Imperial government system. These provinces were under the direct control of a Proconsular Senator, with little need for intervention by the Emperor, though he had the power to appoint these governors if he wished.
The main rule of thumb for Senatorial provinces was, since they were not under the direct authority of the Emperor, that the governors didn't have Legions under their command. There was one exception to this rule in the province of Africa where there was always a single Legion to protect the province from African Berber tribes.
Two of the 10 Senatorial provinces were actually governed by Proconsuls and the remaining eight by Propraetors, but all 10 were always called Proconsul. The Governors of Asia and Africa, the Consuls, served for 1 year and the 8 Praetors served typically for up to 3 years. All of these men had six lictors who served as bodyguards and as a symbol of authority and as a mark of their position. In the Republican system a Consul would have had 12 lictors.
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The distinction between consular (or proconsular) and praetorial (or propraetorial) provinces varied from year to year with the military exigencies of different parts of the empire.