We've come a long way since the world's first skyscraper, the ten-story Home Insurance Building in Chicago, was built between 1884 and 1885. Since then, we've seen iconic buildings rise from construction to completion and become integral parts of a city's skyline: London's Shard, Hong Kong's Bank of China Tower, and New York City's One World Trade Center among them. But in recent years, no city has done boundary-pushing architecture quite like Dubai in the United Arab Emirates. Currently laying claim to the world's tallest building (the Burj Khalifa, at 2,717 feet), the city in 2020 will reputedly have a new tower that surpasses the height of even the Burj.

Designed by Spanish-Swiss architect Santiago Calatrava Valls (whose recent work includes the steel-ribbed Oculus in Manhattan) the new tower is a key element in the redevelopment of old Dubai, and is expected to have rotating glass balconies, residential units and a boutique hotel, a rooftop courtyard, restaurants, and "garden" observation decks replete with trees and other greenery. Mohamed Alabbar, company chairman of Emaar Properties, the government-backed company behind the project, said the tower would be a "notch" taller than the Burj Khalifa, though he wouldn't say how big this "notch" might be. Other numbers of note: The as-of-yet-unnamed tower will cost $1 billion, and is scheduled to be completed for the Dubai Expo trade fair in 2020.

Though the tower could surpass the Burj Khalifa in height, it may not be considered a taller "building" due to architectural specifications that stipulate at least 50 percent of a structure's height must contain usable floor area for it to be under consideration for a ranking of the world's tallest buildings. Preliminary mock-ups show the tower is less a skyscraper and more a cable-supported spire. It might not matter that much, anyway: A skyscraper currently being built in Jeddah, Saudi Arabia, is anticipated to rise 3,281 feet.