An arch is a curved structure that spans an opening and supports weight from above. It is commonly made from materials like stone, brick, or concrete. Arches are often used in architecture to create doorways, bridges, and aqueducts, allowing for both strength and aesthetic appeal. The design of an arch relies on the principle of compression, where the weight is distributed along the curve. Famous examples of arches include the Roman Colosseum and the Arc de Triomphe in Paris. Arches have been used for thousands of years and continue to be a fundamental element in modern construction.