City on the Arno (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">city on the arno</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for pisa that I've seen before include "Italian city with leaning tower" , "Site of the famous leaning tower" , "Location of leaning tower" , "City with listed building" , "Italian city with famous tower" .)