Pianos are so heavy to move and require special movers because of the materials they are made of. The woods used to make pianos tend to be the heaviest, hardest woods such as mahogany, walnut, oak, and birch. The internal frames, usually brass or steel, aren’t light-weight either. They’re sturdy, which is why they last so long when properly cared for. Some of the first actual pianos ever built are still in like-new condition.