How was the Seoul area connected to Baekje during the Three Kingdoms period?

During the Three Kingdoms period, the area now occupied by Seoul was most closely associated with the kingdom of Baekje during its early stages.1

Historical and archaeological evidence indicates that the original site of Baekje’s capital, Wiryeseong, was located in the northeastern part of present-day Seoul. Shortly after its founding, the capital was moved south across the Han River, where various remains—including dwellings, earthen walls, and tombs—have been discovered.1

By the reign of King Geonchogo (346–375 ce), Baekje had expanded its control to encompass the entire Han River basin. However, the region later became a contested borderland between the three kingdoms, and Baekje eventually lost this territory to the northern kingdom of Goguryeo in the late 5th century, forcing the kingdom to relocate its capital further south to Ungjin.21