Spans (6)
(Other definitions for arches that I've seen before include "Extends across" , "(Cat) stretches (back)" , "Found on feet and bridges" , "Search (anag.)" , "Under-parts of feet, sometimes fallen" .)
'spans' is the definition.
('bridge' can be a synonym of 'span')
This is the entire clue.
(Other definitions for bridges that I've seen before include "Robert -, poet laureate" , "One responsible for lyrics" , "links" , "Big reds (anag.)" , "WRITER" .)