First of poems Yeats read, surrounded by an ancient monument (7)
I believe the answer is:
pyramid
'an ancient monument' is the definition.
(I've seen this before)
'first of poems yeats read surrounded by' is the wordplay.
'first of' indicates taking the first letters.
'surrounded by' becomes 'amid' (amid means among or surrounded by).
The initial letters of 'poems yeats read' is 'pyr'.
'pyr'+'amid'='PYRAMID'
(Other definitions for pyramid that I've seen before include "Form of ancient Egyptian royal tomb" , "old tomb" , "Object with polygonal base and triangular sides meeting at point" , "A 3D shape" , "Ancient Egyptian building" .)