Inverted arch indeed a kind of bridge (7)
I believe the answer is:
auction
'a kind of bridge' is the definition.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for auction that I've seen before include "Caution about method of sale" , "Public sale by bid" , "A lot will be seen in this" , "Use caution at public sale" , "Competitive sale" .)