Boast about a century in Polish city (6)
I believe the answer is:
cracow
'polish city' is the definition.
(I've seen this before)
'boast about a century' is the wordplay.
'boast' becomes 'crow' (crow is a kind of boast).
'about' indicates putting letters inside.
'century' becomes 'c' (common abbreviation).
'a'+'c'='ac'
'crow' placed around 'ac' is 'CRACOW'.
'in' is the link.
(Other definitions for cracow that I've seen before include "foreign city" , "E European city" , "Polish city" , "Capital at one time" , "Former Polish capital" .)