Atop the bridge that connects San Francisco Bay to the Pacific Ocean The Golden Gate Bridge is a worldwide recognized symbol of San Francisco and California. It is an engineering marvel, built in four years thanks to remarkable human vision, perseverance, and technological competence. The Golden Gate Bridge is composed of three separate bridges joined by continuous sidewalks. Each section of the bridge is independently strong enough to support its own weight as well as that of all traffic crossing it. This unique design allows for major repairs or replacements to be done on one section of the bridge without affecting the other two. The bridge's construction was made possible by the use of innovative new materials and designs that were not available at the time. For example, the main cables of the bridge are made of stainless steel instead of iron or steel because researchers believed that this material would be less likely to rust. Another example is the fact that the base of each tower is hollow so that cable cars can move up and down them. The bridge's designers also took advantage of its location near the mouth of the bay where the water is quite deep (up to 100 feet), which allowed for its size to be reduced significantly compared with other bridges at the time.