Innovations in construction have significantly sped up development. It’s no surprise that many major projects, such as Dubai's towering skyscrapers and large dams worldwide, are finished in just a few years. Historically, it wasn't unusual for buildings to require decades or even hundreds of years to complete!
Click through the following gallery and build up a picture of some of the lengthiest construction projects in history, and find out what building took the longest to be signed off.