Tenth Century German king to go back and forth (4)

I believe the answer is:

otto

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'tenth century german' is the definition.
'otto' can be an answer for 'german' (common German name). I'm not certain of the 'tenth century' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for otto that I've seen before include "Rose oil; man's name" , "fragrance comes from?" , "Reversible German" , "-- Klemperer, conductor" , "Oil made of rose petals" .)

I've seen this clue in the Sydney Morning Herald.

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