One of my favourites, at the time only recently reopened (*)
The church is in the ancient Roman Velabrum, near the Arch of Janus in the Ripa rione.
Its site near the River Tiber was within a complex of pagan temples from the Republican
era, associated with Rome's port - and the ancient 'Arcus Argentariorum' was incorporated
into its facade.
More background __ http://romanchurches.wikia.com/wiki/San_Giorgio_in_Velabro
(*) For the story of the 1993 car bomb attack which destroyed the portico, and its restoration:
If not otherwise attributed © Peter Bardwell