These days skyscrapers can be found in big cities around the world. It’s easy for us to forget that every single skyscraper is an architectural and engineering marvel, but making them stand safe and sturdy is a difficult task that takes thousands of people to achieve. Skyscraper Day is a holiday to appreciate just how amazing these buildings are and to learn about their history and how they’re made. In order to be classified as a skyscraper, a building must be at least 40 stories high, or about 150 m (492 ft) high. The first building to be called a skyscraper, however, was the 10-story Home Insurance Building in Chicago. It was a precursor to all the skyscrapers to come because it was the first tall building to use a metal frame. Without the metal frame such tall structures wouldn’t be possible. In the early 1900s, architects and cities began competing to see who could build the tallest skyscraper. This is a competition that is still going on today, with taller and taller buildings constantly being built. The current tallest building is the Burj Khalifa in Dubai, but a taller one is already being constructed in Saudi Arabia.