The structural characteristics of four basic types of bridges, beam bridges, arch bridges, cable-stayed bridges, and suspension bridges, were summarized in this paper. A bridge type quadrant diagram was constructed using the orthogonality of beams and piers (towers) and the symmetry of bridge structures. Based on the bridge type quadrant diagram,① It was proven that there are only five basic bridge types. ② The structure and mechanical characteristics of the fifth type of bridge, called the umbrella truss bridge, were summa-rized.③ The structural features of the umbrella truss bridge were analyzed and optimized, leading to the identification of a corresponding real bridge after optimization. The real bridge not only verified the authenticity of the fifth basic bridge structure derived from the bridge type quadrant diagram but also validated the bridge type quadrant diagram proposed in this study. The results of this study provide a valuable attempt and discussion for perfecting and guiding the research and development of theoretical bridges.