PREPOSITIONS. Of redundantOf is sometimes redundant before relatives and relatival words in dependent sentences, mostly after verbs intransitive.
“Make choice of which your highness will see first.
“What it should be . . . I cannot dream of.
“Making just report
Of how unnatural and bemadding sorrow
The king hath cause to plain.
where, however, "whence" is, perhaps, loosely used for "what place," and of strictly used for "from." The redundant and appositional of, which we still use after "town," "city," "valley," &c., is used after "river" (as sometimes by Chaucer and Mandeville) in
“He desires to know of you of whence you are,
“The river of Cydnus.