In my search for a bridge

So, I'm trying to wrap my head around the actual construction of the bridge. I'm not talking about the bridge design. I've found plenty of information on the Kingpost Truss bridges with regards to the design and there are lots and lots of wonderful pictures of the old covered bridges. (I'll list a few at the end of this post) I'm talking about the actual construction. How did they erect bridges across wide rivers in the 1870's?

I ordered a DVD on the topic and hope it will shed some light, but in the meantime, I've had some wonderful discussions with my DH. He's a very talented weekend carpenter who works with engineers during the day, so he's been talking me through the process. He thinks they probably strung a guideline across the river to help position boards onto the stone pilings. Notches would have been cut into the side rails for the trusses to slip into. The trusses were connected with a pin hinge. Well, okay, not to bore you, I found it all quite fascinating. Have you ever watched an episode of the New Yankee Woodshop? Try imagining building something this big with limited tools and resources. It's not like these builders could run to the local Lowes or Home Depot for more nails. LOL

Okay, so here's the DVD I bought: Spanning Time: America's Covered Bridges or here's one on covered bridges in Indiana.

I also spent time researching cast iron, wrought iron and steel bridges. I was very happy to discover that the first steel bridge in America was built in 1874 across the Mississippi, but this works perfectly into my story as the hero's goal is to develop his own engineering company building steel bridges. Yup, this story is shaping up nicely. :-)