That was Lex’s reaction to this photo:
Click the photo to see it at larger size with historical information.
More photos and information here.
UPDATE: Much more info about the bridge and railway line here (courtesy of Lex). Also, see the comments for some juicy book references.
UPDATE 2: Via Tim Worstall comes this fascinating story about railway construction across the Andes. (Check out the rest of the railway history site too.)