Sparta built by old governor (6)
I believe the answer is:
satrap
'old governor' is the definition.
(I've seen this before)
'sparta built' is the wordplay.
'built' indicates an anagram.
'sparta' with letters rearranged gives 'SATRAP'.
'by' is the link.
(Other definitions for satrap that I've seen before include "Sparta (anag.)" , "A sprat for the old governor of Persia" , "local ruler" , "Old Persian governor took a seat to start" , "despotic ruler" .)