Classical colonnade (4)
I believe the answer is:
stoa
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">classical colonnade</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for stoa that I've seen before include "Venue for Greek philosophers" , "Where Zeno spoke" , "classical colonnade" , "old school" , "Roofed colonnade (Gr.)" .)