The competition to erect the world's tallest building and the engineering challenge of great height have been continuing themes over the century. What drives structures ever higher? Technology, economics, ego? While advances in technology made taller buildings possible, architects and engineers can design safe structures much taller than clients will build. Supertall skyscrapers are expensive propositions, and their balance sheets are carefully drawn. An owner or developer weighs the high cost of additional stories against the anticipated rents or other benefits -- including the publicity and prestige associated with premier height.

Why is the idea of tallest so captivating? Announcements of new projects grab headlines. Television documentaries on the topic multiply. Bragging rights become a point of urban and national rivalry, and standards for how to measure heights must be refereed by professional associations.