Roman god of doorways, passages and bridges (5)
I believe the answer is:
janus
(Other definitions for janus that I've seen before include "Two-faced god of gates and doors - Guardian cryptic crossword setter" , "Two-faced Roman god who guarded doors and gates" , "Roman god of doors and beginnings" , "Two-faced deity" , "Roman god of doors, usually two-faced - a month is named for him" .)