Period of historic hierachy? (3)

I believe the answer is:

era

'period' is the definition.
(I know that era is a type of period)

'of historic hierachy?' is the wordplay.
'of' indicates a hidden word.
'ERA' is hidden in the letters of 'historic hierachy'.

(Other definitions for era that I've seen before include "Are involved in time span" , "Geological age" , "Distinctive period of time" , "Period of alteration" , "Important date" .)

I've seen this clue in the Evening Standard.

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