Records show that while the area around Seoul has been settled from the Paleolithic Age, the city wasn't officially founded until 18 BC when the kingdom of Baekje built its capital city Wiryeseong at the site. In time, Baekje developed from a small minor state into one of the major Three Kingdoms of Korea, a group of countries which dominated the peninsula for most of the first millennium. Over time, Seoul grew into a formidable city and held great political significance.
Eventually the Three Kingdoms were consolidated under one rule, and in 1394 AD the capital of this new country was moved to Seoul. Large walls were built around the city, as much to keep out thieves as well as tigers and other unwanted large, scary animals. Each day the gates were opened at dawn and closed at dusk, keeping the city isolated and protected. Eventually, Seoul opened its gates to the influx of westerners arriving in the east during the late 1800's, and the city began to modernize. In fact, Seoul was the first eastern city to have electricity, running water, and the telephone.
Things continued well for Seoul until World War I when the Japanese occupied Korea in 1910; the country remained under Japanese rule until 1945. After Korea's liberation, the Republic of Korea was founded (modern day South Korea), and Seoul was named as its capital. During the Korean War, starting in 1950, Seoul changed hands between North and South Korea many times, it being less than 100 miles from the border. The city endured heavy damage during this time, with over two hundred thousand buildings in ruins.
After the war, the city was the focus of a huge reconstruction effort and an attempt to improve the standard of living for the population, which had swelled with millions of refugees. The city continued its population and economic boom into the 21st century, becoming the third largest metropolitan area in the world and housing a full quarter of South Korea's population. Seoul has been voted the 2010 Design Capital of the World, boasts one of the world's most technologically advanced infrastructures, and is home to some of the world's largest electronic companies.