I thought a bridge was just a decorative part of the movement

Yes. Bridges are structural. They support the pivots of the gear train and keep everything in alignment. On a skeleton watch you see them more clearly, but they're doing real work.

The decoration is usually on the surface, but the shape and thickness are engineered. If a bridge were purely decorative, the movement wouldn't run.

I used to think the same thing until I saw a movement diagram. The bridges are basically the frame. The skeletonizing just removes material where it isn't needed, so you can see through.

Wait, so are all those fancy angles and bevels on the bridges just for looks? Or do they affect how the movement works?

Beveling is mostly finishing, but it can remove burrs and stress points. The geometry of the bridge matters more than the polish, though.

This is why cheap skeleton watches can be a gamble. If the bridges are thinned too much for looks, the pivots can shift and the movement loses accuracy.

I had a cheap one where a bridge was visibly bent. It still ran, but the amplitude was terrible.

That's a good point. Skeletonizing is a trade-off. You remov material for visibility, but you need to keep enough rigidity.

So the bridge is structural, not just decorative. I need to look at my watch differently now. Thanks for clearing that up.