Relative to the Korean peninsula, the sea routes of East Asia from ancient times to the Goryeo period were the coastal sea route and the crosscut and oblique routes of the Yellow Sea. The coastal sea route was a major sea route until the crosscut and oblique sea routes became commonly used during the Unified Silla period.
The coastal sea routes during the Three Kingdoms period can be divided into the southwestern route and southeastern route. Travelers along these coastal sea routes utilized various coastal islands for island hopping.
Due to fierce competition among the Three Kingdoms in the mid-6^th^ century, the southwestern coastal sea route was blocked and cultural exchange in East Asia halted for a long period. As a result, the conflict among the Three Kingdoms was regarded as a serious problem beyond the Korean Peninsula and ultimately led to the Tang Dynasty and Japan joining in the conflict.
In 660, a general of the Tang Dynasty, Su Dingfang led his troops across the Yellow Sea, following a sea route that was known to be the most dangerous. It is noteworthy that on this voyage he hopped island, utilizing islands that included Deokmuldo (Deokjeokdo). From then on, the crosscut and oblique sea routes of the Yellow Sea were utilized as regular sea routes along with the costal sea route. This diversification of sea routes then contributed the burgeoning of maritime activity during the Unified Silla and Goryeo periods. Several documents at that time describe various islands that were used for island hopping.