The Kofun era and early state formationThis autonomous nature of local polities in the fifth century may also be reflected in different
patterns of interaction between the central polity and various local polities. In a few cases, the
central polity maintained a kind of gunboat diplomacy, wherein the Yamato court dispatched
influential military leaders who were later buried with dozens of sets of iron armor in stone
coffins of the same style as the central chieftain. In most cases, the central chieftain apparently
gave additional armors to second- ranking local chiefs as well. Indeed, in fifth century sites in the
Kanto, iron armor is often discovered in small circular mounds, rather than in large keyhole-
shaped tumuli. It is possible that the central polity tried to lure the attention of the highest
ranking local chiefs far away from the Kinai. In still- other instances, the central polity may have
simply given out symbolic titles to local elites.^28
In this period, while the construction of keyhole- shaped burial mounds was just getting
started in some regions, it temporarily ceased in others. It may be possible to interpret the former
cases as reflections of a phenomenon in which local elites finally became incorporated into a con-
federation led by the central polity. For the latter cases, I would propose the possibility that local
polities came to be temporarily separated from the confederation.
The Late Kofun era
In the sixth century—the Late Kofun era—society transformed drastically, as is clearly reflected
in several major changes in mortuary practices. These changes include a decline in the construc-
tion of large keyhole- shaped tumuli, a drastic increase in the construction of minor circular burial
mounds in clusters (referred to as gunshūfun), and the adoption of corridor- style horizontal burial
chambers (referred to as yokoana- shiki sekishitu) that could be opened for additional interments
after the initial burial.
While the decline in the construction of keyhole- shape tumuli indicates that such tombs came
to be restricted to fewer, and even higher- ranking elites, the appearance of gunshūfun indicates
that far more people came to be buried in mounded tombs in the Late Kofun era than before.
Scholars interpret gunshūfun as a reflection of the central polity incorporating more people into
its own social system, and of more people rising to the social class that allowed them to be buried
in mounded tombs.^29 It may also be that ideology of the central polity changed, and keyhole-
shaped tumuli were no longer as important as symbols of power as they had been in the Early and
Middle Kofun eras.
The adoption of the corridor- style horizontal burial chambers was important because the size
of the chamber would become a status symbol, regardless of the form and size of the tomb itself.
This drastic change may have been initiated by King Keitai (r. 507–531 or 534). For the first time
in the Kofun era, burial chambers of the same structure and style were constructed in all mounded
tombs, from the largest keyhole- shaped tumuli—such as Keitai’s own—to small circular tombs
less than 20 meters in diameter.
The adoption of the corridor- style horizontal burial chamber was in a sense inevitable, because
kinship structure changed in the early sixth century. According to a very innovative study by
Tanaka Yoshiyuki (1953–2014), while brothers and sisters had been buried together until the
beginning of the sixth century, fathers and children who were not selected to be the heir came to
be buried together from the early sixth century on. From the middle sixth century, mothers were
also buried with their husbands.^30 In other words, burial chambers had to have a structure that
would allow additional interments, resulting in a corridor- style burial chamber that could be
reopened later.
From the middle sixth century, the assemblage of grave goods to some extent determined the
social status of elites, which was correlated to the size of corridor- style horizontal burial chambers.