Study elevated position, circling ancient city in choppers (8)

'choppers' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Perhaps they are linked in a way I don't understand?

'study elevated position circling ancient city' is the wordplay.
'study' becomes 'den' (term for a study or office).
'elevated' is a reversal indicator (in a down clue, letters go up).
'position' becomes 'set' (setting is a kind of positioning).
'circling' means one lot of letters goes inside another (circling can mean going around or containing).
'ancient city' becomes 'ur' (ancient Sumerian city state).
'set' in reverse letter order is 'tes'.
'tes' placed around 'ur' is 'tures'.
'den'+'tures'='DENTURES'

'in' acts as a link.

Can you help me to learn more?