The towers are bolted to stone masonry piers. Diagonal elements provide lateral stability to the four tower legs. Floor beams are at each vertical member and support a concrete deck. I like the lace-like railing on the deck. I wonder if it was part of the original structure or if it was added later?
It seems strange to have such a long viaduct just to cross the Rio Chili. Perhaps it was economical to build a 500 meter long viaduct so that the track could maintain it's grade across the valley. In the map below, we can see to the east of the bridge an railroad yard and train station whose tracks used to go onto the bridge.
Peru's Bridges: Puente Bolivar (3) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.