Early pianos were made with wooden frames, which limited the amount of tension the strings could hold. As composers like Beethoven demanded more volume and power, the physical limits of wood were pushed to the breaking point. In 1825, Alpheus Babcock patented the first one-piece cast-iron frame in Boston. This innovation was revolutionary because it allowed the strings to be stretched at much higher tensions—eventually reaching over 20 tons of total force in a modern grand piano. The iron frame prevented the piano from warping or collapsing under this immense pressure and allowed for thicker strings and larger hammers. This resulted in the brilliant, sustaining, and powerful sound we associate with the modern concert grand. Without the cast-iron plate, the massive virtuoso concertos of Liszt and Rachmaninoff would have been physically impossible to perform on the instrument.