Seoul (, /soʊl/, "Capital City", from ancient Sillan "Seorabeol"), officially the Seoul Special City, is the capital and largest metropolis of South Korea. A megacity with a population of more than 10 million, it is the largest city proper in the OECD developed world. The Seoul National Capital Area, which includes the surrounding Incheon metropolis and Gyeonggi province, is the world's second largest metropolitan area with over 25 million people, home to over half of South Koreans along with 366,000 international residents.

Situated on the Han River, Seoul's history stretches back more than 2,000 years when it was founded in 18 BCE by Baekje, one of the Three Kingdoms of Korea. It continued as the capital of Korea under the Joseon Dynasty and the Korean Empire. The Seoul National Capital Area contains four UNESCO World Heritage Sites: Changdeok Palace, Hwaseong Fortress, Jongmyo Shrine and the Royal Tombs of the Joseon Dynasty. Seoul is surrounded by mountains, the tallest being Mt. Bukhan, the world's most visited national park. Modern landmarks holding Guinness World Records include Lotte World, the world's largest indoor theme park, Moonlight Rainbow Fountain, the world's longest bridge fountain and Times Square's CGV Starium, the world's largest cinema screen. Seoul was voted the top travel destination by Chinese, Japanese and Thai tourists for a third consecutive year in 2011.

Today, Seoul is considered a leading and rapidly rising global city, resulting from a period of rapid economic growth known as the Miracle on the Han River which transformed it from the ashes of the Korean war to the world's fourth largest urban agglomeration economy with a GDP of US$703 billion at purchasing power parity in 2010 after Tokyo, New York City and Los Angeles. It hosts the world's sixth largest number of Fortune Global 500 multinationals such as Samsung, LG and Hyundai-Kia. Forbes lists Seoul as the world's sixth most economically powerful city and it is ranked sixth in the 2012 Global Financial Centres Index, surpassing Tokyo by rising three places from 2011. The metropolis is involved in many global affairs, exerting a major influence as the host of the fifth most global conferences worldwide.

Seoul has much technologically advanced infrastructure. It has the world's highest fibre-optic broadband penetration, resulting in the world's fastest internet connections with speeds up to 1Gbps. Seoul was the world's first city to introduce Digital Multimedia Broadcasting for television and radio, and WiBro for data, both serviced in all subway lines along with 4G LTE and WiFi. Seoul Station is the main terminal of the KTX High-speed rail and the Seoul Subway is the world's second most highly used with the longest circular line in the world. It is considered the world's best subway system noted for its cleanliness and easy of use, and unique in having all stations installed with automatic platform gates. Seoul shares a unified public transportation system with neighboring Incheon and Gyeonggi allowing passengers to transfer freely from subway or bus using the T-money smart card, and is connected via AREX to Incheon International Airport, rated the best airport worldwide since 2005 by Airports Council International.

Seoul hosted the 1986 Asian Games, 1988 Summer Olympics, 2002 FIFA World Cup and the 2010 G-20 Seoul summit. The city was named the World Design Capital for 2010.

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