Row about black river in Italy (5)
I believe the answer is:
tiber
'river in italy' is the definition.
(river that flows through Rome)
'row about black' is the wordplay.
'row' becomes 'tier' (a tier is a row of things).
'about' is an insertion indicator.
'black' becomes 'b' (abbreviation as in pencil classifications).
'tier' going around 'b' is 'TIBER'.
(Other definitions for tiber that I've seen before include "The flower of Rome" , "divides Rome" , "Italian banker" , "Roman river" , "River of Rome" .)