Core and Periphery in the Bihwagaya as Reflected in Burial Mound Construction Techniques

The burial mound builders of Bihwagaya can be broadly divided into two groups: the builders of the Gyesong Tomb Group and those of the Gyodong-Songhyeon-dong Tomb Groups. The Gyesong Tomb Group features large earthen mounds arranged in linear patterns along ridge lines. The mounds are typically oval in shape and encircled by double-layered stone settings (hoseok). The construction of the mound fill follows a sequential layering method, with partitioning achieved through stone alignment structures. The burial system begins as a pit-style tomb with compartment walls dividing the main and subsidiary burial chambers, and transitions into a horizontal entrance style (hoenggushik) with secondary burials after the 6th century. For the stone-lined pit graves, natural flat stones (cheonseok) were primarily used, along with wooden elements and horizontal timbers as auxiliary structures. The tomb orientation is generally north-facing. Subordinate to the Gyesong group are peripheral tomb clusters such as the Yeongsan and Ugang-ri tomb groups. In contrast, the Gyodong and Songhyeon-dong Tomb Groups consist of clusters formed by both large and small to medium-sized mounds. The tombs are circular in shape, often accompanied by eyebrow-shaped moats (jugus). The stone settings are aligned in a single row, with some mounds showing a two-tiered structure. The mound fill method includes simultaneous and segmented layering, with various partitioning techniques such as ridge-style divisions, clay blocks, marker stones, stone alignments, and wooden posts. The burial system is of the horizontal entrance type, typically with no subsidiary chamber, and features an entrance on one side. The walls of the burial chambers are constructed with horizontally or vertically laid stones, and wooden posts and horizontal beams are used as supplementary structural elements. The tomb orientation is south-facing. Traces of ritual activity, such as the burial of animal bones near the entrance, have been identified. Peripheral tomb clusters subordinate to the Gyodong and Songhyeon-dong groups include the Ucheon-ri, Chogok-ri, and Jumae-ri Masan site tomb groups, as well as the Seonggok-ri, Bonggi-ri, and Songseo-ri groups in the Cheongdo region. The Ugang-ri Tomb Group, initially subordinate to the Gyesong group, later came under the influence of the Gyodong and Songhyeon-dong groups in its later phase of mound construction. Based on construction techniques, burial rituals, and shared pottery culture, the core region of Bihwagaya is considered to correspond to the current administrative areas of Changnyeong-eup, Gyesong-myeon, Yeongsan-myeon, Daehap-myeon, Docheon-myeon, and Ibang-myeon in Changnyeong County, as well as Punggak-myeon in Cheongdo County. The incorporation of Bihwagaya into the Silla state is thought to have occurred sometime between the early 6th century— when tombs such as SongI-6·7 and GyoI-12 were constructed and the mid-6th century, when Silla’s administrative expansion is documented through historical records and the erection of King Jinheung's boundary monuments.