In 1709, Italian Cristofori invented the piano. Its core design was the use of hammers to strike the strings and the resulting tuning system. This solved the harpsichord's inability to change volume by key pressure, allowing for a dynamic shift between "light" (piano) and "loud" (forte). In the mid-18th century, German Silbermann improved the hammers and added a damper pedal. The light pianos produced by the Viennese School were favored by Mozart for their sensitivity. In the 19th century, the Broadwood Company expanded the range and reinforced the piano frame. In 1825, a cast iron frame solved string tension issues. Cross-string technology enhanced resonance. A double escapement mechanism enabled rapid legato, satisfying the needs of Romantic composers. In the 20th century, the piano was formalized into two types: grand and upright.