The tallest building in the world, Burj Khalifa, was officially opened in Dubai, United Arab Emirates, on January 4, 2010. Standing 829.8-metre (2,722-feet) tall, the skyscraper was known as Burj Dubai before its inauguration. The construction of the building started in 2004 and cost $1.5 billion. The concrete's weight used to build Burj Khalifa was reportedly equivalent to 1,00,000 elephants.