As emperor, he had his own column (6)
I believe the answer is:
trajan
'his own column' is the definition.
The definition suggests a singular noun which matches the answer.
'as emperor he' is the wordplay.
I cannot really understand how this works, but
'he' could be 'jan' and 'jan' is found within the answer.
The remaining letters 'tra' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'had' acts as a link.
Can you help me to learn more?
(Other definitions for trajan that I've seen before include "Roman emperor, ruled 98 to 117 AD" , "Roman emperor of column fame" , "Roman emperor AD ninety eight to AD one hundred and seventeen" .)