The Willis Tower (formerly and informally: Sears Tower, its title until 2009) is a 110-story, 1,450-foot (442.1 m) skyscraper in Chicago. At completion in 1973, it surpassed the World Trade Center in New York City to become the tallest building in the world, a title that it held for nearly 25 years; it was also the tallest building in the Western Hemisphere for 41 years, before the new One World Trade Center surpassed it in 2013. While it held the title of'Tallest Office Building' before 2013, it dropped the title of'Tallest Man-Made Construction' after only 3 decades. The CN Tower in Toronto, which functions as a communications tower, took over the title in 1976.
The Willis Tower is considered a seminal accomplishment for engineer Fazlur Rahman Khan. It is currently the third-tallest construction in the USA and the Western hemisphere -- and the 23rd-tallest in the world.
The Messeturm, or Trade Fair Tower, is a 63-storey, 257 m (843 feet ) skyscraper at the Westend-Süd district of Frankfurt, Germany. It is the second tallest building in Frankfurt, the second tallest building in Germany and the second tallest building in the European Union. It was the tallest building in Europe from its completion in 1991 until 1997 when it was surpassed by the Commerzbank Tower, which is also situated in Frankfurt. The Messeturm is the 17th tallest building in Europe and the 413th tallest in the world.The Messeturm is located close to the Frankfurt Trade Fair grounds. Helmut Jahn made the Messeturm in a postmodern architectural style. It is regarded as one of the design classics among European skyscrapers. Despite its name, the Messeturm isn't used for trade fair exhibitions but as an office building. It is one of the few buildings in Germany with their own postal code (60308), the others being Opernturm, another Frankfurt skyscraper, and the summit station on Zugspitze.Source: Wikipedia