|Silla occupied Jin-han chiefdom societies(辰韓 諸國) from the end of the 3rd century to the beginning and grew into an antient territorial state. But Silla did not directly rules out the conquest area, and maintained its indirect dominance. Silla implemented four indirect dominance, a tributary payment which was the most common rule among them.
The reason was that Silla stayed under the intervention of Goguryeo in the first half of the 5th century. After King Noolji`s reign, Silla was reorganized with a unified hierarchy of rulers, was reorganized as a controlling system centered around the king. After the implementation of local system in 505, Silla began direct regional rule by sending officials and armed forces to provincial areas. Based on the inscriptions in connection with local rule, Silla had a local reign system and exercised local rule since 540s.
Although the Busan area as Dokroguk was incorporated into Silla in 460s, the Busan area excluding Kijang was still indirectly ruled by Silla. Silla used Kijang as a naval base Imhaejin to prevent from invasion of ancient Japan. Dongnae area including Yeonsandong tombs as the center of Dokroguk was organized under direct rule of Silla since Geumgwan Gaya surrendered to Silla in 532.
In conclusion, Silla was able to systematically reign Dokroguk by 540s, the former Busan area maintained its own identity. Therefore, Yeonsandong tombs under 540s must be the remains of Gaya`s cultural heritage.