Imperial backer of art at the year's start (6)
I believe the answer is:
trajan
'imperial backer' is the definition.
The definition suggests a singular noun which matches the answer.
'of art at the year's start' is the wordplay.
'of' is an anagram indicator (the answer comes from or 'of' the letters).
'at' says to put letters next to each other.
'the year's start' becomes 'jan' (I can't explain this - if you can you should give a lot more credence to this answer).
'art' with letters rearranged gives 'tra'.
'tra'+'jan'='TRAJAN'
Can you help me to learn more?
(Other definitions for trajan that I've seen before include "Roman emperor AD ninety eight to AD one hundred and seventeen" , "Roman emperor of column fame" , "Roman emperor, ruled 98 to 117 AD" .)