Gallon House Covered bridge

Wayne and I wanted to get out and take a little drive today. We wanted to go some place different- some place interesting, and we didn't want food or shopping to be the focus. He came up with the bright idea that we should find a covered bridge. There are quite a few covered bridges in Oregon, but we've never looked for them. So.... we got onto the internet and found that a the Gallon House covered bridge is a little more than an hour away (or longer if you take back roads like we did today). The Gallon House covered bridge is on Gallon House Road (brilliant!) somewhere between Mt. Angel and Silverton, Oregon. It's probably in one of those cities but we couldn't figure it out because it was pretty rural. It bridges a little creek, with farm land on both sides- mostly hops. The original bridge was built in 1916, and some restoration work was done in recent years. The story goes that there was a house somewhere near the bridge where you could get alcohol during prohibition- and it was sold by the gallon. I'm not sure that's true- but that's the story. Very cool! I think I can get into this! I want to find another one the next time we want to take a drive. I might even end up with a covered bridge quilt one of these days. I have done some searching and every covered bridge that I found has lots of history. But I still have one question- why covered bridges? Can anyone tell me the purpose of covering a bridge? They look cool, but I don't get it. Any covered bridge experts out there?