Authoritarian rule can be or cannot be legitimate because existence of pure legitimacy is not possible
Explanation:
The legitimacy represents outspoken public loyalty and conformist mentality of a individual /group/organization which shapes the repressive administrative machinery to be of a high developed nature. This is not possible in authoritarian regimes which leverage to facilitate certain sects of the society like elite group.
However, in current time pure legitimacy is also not possible hence the concept of authoritative legitimacy is arising.
It was manly because of the catholic church which remained in the base of Rome. It drew pilgrims from all over Europe, educated clerics to read and write, support arts and architecture.