More than 2,000 years after it was built, the Pantheon has stood the test of time. Its un-reinforced concrete dome has been influential to designers since its completion. In Italy 1,000 years after the Pantheon was finished, workers spent a century building the most magnificent cathedral they could, but there was one main problem: there was no roof and no one knew how to build one. The designer drew inspiration from the Pantheon, but there was no mixture of concrete at the time. Instead, bricks were the only material available to him. Eventually, the designer came up with an ingenious feat without using any scaffolding, and the dome of the Florence Cathedral still stands today as a testament to this engineering.
　　A more recently built dome is the Houston Astrodome, which was renowned as an architectural triumph in 1965. The main reasons for its praise were its lightweight roof and Astroturf—a new term for artificial grass. Nearly 30 years later, engineers were very concerned about public safety when it came to fires in crowded places. The Georgia Dome included an advanced ventilation system that could suck smoke out in case of an emergency when it became the home of the Atlanta Falcons in 1992. But what do all these domes have in common? They have all greatly influenced the Oita Dome in Japan.
　　The Oita Dome is the pinnacle of structural engineering as the largest freestanding dome in the world. It has taken bits and pieces of each structure mentioned and combined them to make the dome of the future. The roof spans 274 meters, and the stadium can seat 43,000 fans. If the weather changes, one click of a switch and the dome closes so that the sporting event and its spectators won't be affected. This month, the National Geographic Channel goes inside the Oita Dome and learns the incredible story behind it with Big Bigger Biggest 2: Dome.