Old habits being what they are, I could not put up a page about a bridge without explaining how it works. Mr. Leonardo has checked this page for me and says I have it right, which I would like noted, since he corrected me twice on the first draft.

1. Why were covered bridges covered?
Not for the horses, and not for the courting, whatever you may have heard. They were covered to keep the bridge dry. The part of a wooden bridge that does the work is its frame of heavy timbers, the trusses along each side. Leave those timbers out in the rain and sun, soaking and drying and soaking again, and they will rot through in perhaps twenty years. Put a roof over them and boards along the sides, and the same timbers can last well over a hundred. The roof and the siding are cheap and easy to replace; the frame is not. A covered bridge is simply a wooden bridge wearing a raincoat.

That said, people did find other uses for the cover. A horse that was skittish about water could not see the creek below. Travelers waited out storms inside. Notices and advertisements were tacked to the walls. And couples found that the middle of a covered bridge was a fine private place, which is why some people call them kissing bridges. I am a witness.

2. What is a truss?
A truss is a frame made of triangles. A triangle is the one shape that cannot be pushed out of shape without breaking one of its sides, so a frame built of triangles is very strong for its weight. The simplest bridge truss is the kingpost: one upright post in the middle, with two slanting braces from its top down to the ends, making two triangles. For a longer bridge, builders lined up many posts and braces in a row, which is called a multiple kingpost truss.

3. What is a Burr arch truss?
In the early 1800s a builder named Theodore Burr took a multiple kingpost truss and added a great curved wooden arch on each side, its two ends set down into the stone abutments below the floor and its middle rising nearly to the roof, bolted to every post it crosses. The truss keeps the arch from bending out of shape, and the arch carries much of the weight down into the abutments. Each helps the other. The design let builders span much longer distances in wood than a truss alone could, and it is the most common kind of covered bridge in Indiana. The Bethel Ford bridge is a fine one: one span of 120 feet, without a single pier in the creek.

Abutments

The stone walls at each end, on the creek banks, that hold the whole thing up. Ours are cut sandstone, laid in 1883 without mortar in the old way, and they have not moved an inch.

Lower chords

The long, heavy timbers that run the full length of the bridge along the bottom of each truss. The floor beams rest on them. These are what rotted at the south end, under the leaking gutter.

Upper chords

The matching timbers along the top of each truss.

Posts and braces

The uprights and the slanting timbers between the chords that make the triangles.

Arches

Each arch is built up of several layers of thick planks, bent to the curve and bolted together. You can see them on the inside walls of the bridge, sweeping up from the floor at each end.

Floor beams and floor

Heavy oak beams laid crosswise on the lower chords, and plank flooring on top of them. The floor was last replaced in 1964.

Siding, roof and portals

The raincoat. Red board siding, a tin roof put on in the 1930s over the old wood shingles, and a white portal, the arched entrance, at each end.

4. The timbers
The 1883 contract, which Mrs. Tallant found in the courthouse, called for the trusses and arches to be of yellow poplar and the floor beams of white oak, all of it "sound and free of rot and wane." Poplar grew tall and straight in the creek bottoms here, and it is light and strong and easy to work. The contract price for the whole bridge, stone and all, was a little under four thousand dollars.

5. Why bridges rot, and how they are mended
A covered bridge rots for one reason: water gets in where it should not. A leaking roof, a clogged or broken gutter, missing siding boards, or brush and silt piled up against the ends of the timbers will do it. The lower chords suffer first, because water runs down to them and because they are closest to the damp of the creek.

Rotted timbers can be mended. Builders who know old bridges support the bridge from below on temporary timber cribbing set in the creek bed, cut out the rotted sections, and splice in new timber of the same size, joined the old way. It is careful, slow work, and it is done on old bridges every year. It is not done by a bulldozer.

6. Indiana's covered bridges
Indiana once had hundreds of covered bridges. Floods, fires, neglect and new highways took most of them, and fewer than a hundred are left in the whole state. Parke County, not far from us, has thirty-one of them and a covered bridge festival every October that brings visitors from all over the country. Every one of those bridges was once somebody's ordinary road to church. So is ours.