CLARKSBURG, W.Va. (WBOY) — West Virginia has 17 historic covered bridges, but no new ones have ben built in the last 120 years for a very specific reason.

Although beautiful, covered bridges don’t make a ton of sense when using modern building materials. In the 1800s when wood was the primary building material, the bridges built were almost completely enclosed to prevent them rotting.

But when iron became more affordable in the mid-1800s, architects realized that metal trusses didn’t need the same protections from the elements that wooden ones did, according to Ancestral Findings. Fully wooden bridges are also expensive to maintain and more susceptible to fires and flooding.

Of the more than 12,000 covered bridges that were build in the U.S. from roughly 1820-1900, fewer than 1,000 are still standing. Several of the remaining 17 covered bridges in West Virginia have been basically rebuilt due to fire, including Philippi Covered Bridge—the state’s oldest and only two-lane bridge—and the Carrollton Covered Bridge, which just reopened this year after being mostly destroyed in an arson in 2017.

Although about half of the bridges are no longer open to vehicle traffic, they still show an important part of the state’s architectural history. You can learn more about the history of each remaining West Virginia bridge on the West Virginia Department of Transportation’s website, and a map of the remaining bridges’ locations is available below.