The founding of Baekje in 18 BCE by King Onjo, a son of Jumong, the founder of Goguryeo, marks a pivotal turning point in ancient Korean history. After the establishment of Goguryeo, when Jumong's eldest son, Yuri, returned from Buyeo, Onjo and his elder brother Biryu decided to seek new lands due to concerns over the succession to the throne. This decision reflected a strong will to build a new nation alongside the growing power of Goguryeo. At that time, the Han River basin was a fertile and strategically important area, home to various small Mahan states, but lacked a unified, powerful entity. Onjo and Biryu led their respective groups south. Biryu settled in Michuhol (present-day Incheon), a coastal area, while Onjo established his capital in Wiryeseong (present-day Songpa District, Seoul), an inland region. However, Michuhol's land was barren and saline, making it unsuitable for agriculture, and the people's lives were difficult. In contrast, Wiryeseong, situated along the Han River, boasted abundant resources and was ideal for farming. It also offered strategic advantages for integrating the surrounding Mahan states. Eventually, Biryu regretted his choice and died, and all his people joined Onjo. Onjo initially named his kingdom "Sipje" (十濟), meaning "ten people crossed," referring to his ten founding ministers. Later, he renamed it "Baekje" (百濟), signifying that "a hundred people (or all people) gladly crossed" or "all people followed." The founding of Baekje signaled the emergence of a powerful ancient state in the central Korean Peninsula. The geographical advantage of the Han River basin played a crucial role in Baekje's ability to boost agricultural productivity, engage in active maritime trade with China, and adopt advanced culture and technology. This laid the foundation for Baekje to grow into a major player alongside Goguryeo and Silla during the Three Kingdoms period. Baekje flourished with brilliant culture and art, and profoundly influenced East Asian history by transmitting Buddhism and advanced techniques to Japan. King Onjo's determination and wisdom initiated the magnificent thousand-year history of Baekje.