I took the first photo with my iphone while attending a business conference in Frankfurt two years ago. Photo #2 is a recent one from May 2019.
The Frankfurt Conference Center Tower (Messeturm) skyscraper was finished in 1991 and is 256 meters or 63 stories tall. The tower was designed by Helmut Jahn, the world-renown architect and CEO of the Chicago-based architecture firm JAHN. Helmut Jahn moved from Germany to Chicago in 1965.
It is truly a "small world" when it comes to the architects of the world's tallest skyscrapers.
The Chicago offices of Helmut Jahn are on the top floors of 35 East Wacker Drive. In photo #2 you see it on the left: it is the concrete and stone building with Greek pillars and dome at the top. At the time of it's completion in 1927, the Jeweler's Building (as it was called then) was the tallest building in Chicago with 40 stories. Now it is directly across from the current title holder, the Trump Tower, which has 98 stories.
When you see these two buildings directly across from each other you can begin to appreciate the advances in engineering, construction and technology which made a more than 100% increase in height possible for skyscrapers in less than 100 years.
Anyone who has flown through Chicago O'Hare airport might have seen the work of Helmut Jahn since he designed the United terminal. He has designed many famous buildings not only in downtown Chicago but also throughout the world.