Kofun period

Kofun came in several shapes – round, square, and the distinctive keyhole form (zenpō kōen fun), combining a square front with a round rear mound where the burial chamber lay. The keyhole mound appears first around the middle of the third century at Makimuku in the Nara Basin, with the Hashihaka Kofun, and spread with remarkable uniformity, suggesting that local elites adopted it as a sign of alliance with Yamato. Its size seems to have reflected rank.

Early tombs had vertical stone chambers holding a wooden coffin, bronze mirrors, jewels and swords; from the late fifth century, horizontal passage chambers (yokoana-shiki sekishitsu) that could be reopened for later burials became common, and grave goods included horse trappings, armour and stoneware. Construction of large keyhole mounds ceased around the end of the sixth century in the Kinai.

The Yamato polity was not yet a centralised state but a hierarchy of alliances. Its rulers styled themselves great kings (ōkimi); the title tennō (emperor) came only in the seventh century. In the fifth century five successive 'kings of Wa' – San, Chin, Sei, Kō and Bu – sent envoys to the Chinese Southern Dynasties seeking recognition and military titles over parts of the Korean peninsula. Bu is generally identified with the ruler later known as Emperor Yūryaku.

Two inscribed swords confirm the reach of this kingship: the Inariyama sword from Saitama Prefecture, dated by most scholars to 471, and a sword from the Eta Funayama mound in Kumamoto both name the great king Wakatakeru (Yūryaku). Power was never uncontested. In 527 Iwai, a powerful chief in northern Kyushu, rose against Yamato in alliance with the Korean kingdom of Silla; his defeat strengthened royal control over the west.

Kofun society was organised around powerful kin groups called uji, each led by a chief and claiming descent from a common ancestor deity. The court assigned them hereditary titles (kabane) such as omi and muraji, and specialised occupational groups (be) – potters, weavers, smiths, scribes – served the court and the great clans. Great families such as the Mononobe, responsible for arms and ritual, the Ōtomo and, from the sixth century, the Soga dominated court politics.

Most people were farmers living in pit dwellings; the elite lived in large enclosed residences. The labour required to build the great mounds – by modern estimates, many hundreds of thousands of working days for the largest – shows the capacity of rulers to mobilise communities.

The Kofun period was shaped by close ties with the kingdoms of the Korean peninsula – Baekje, Silla, Gaya and Goguryeo. Yamato sought iron, which came above all from the Gaya region, and in return provided military support to allies. The Gwanggaeto Stele, erected in 414 in present-day northeast China, records Wa forces fighting on the peninsula, though the extent of their involvement is debated.

Migrants from the peninsula (toraijin) brought decisive skills: high-fired grey stoneware (Sue ware) from the fifth century, advanced iron forging, horse breeding and riding, sericulture and weaving, irrigation works and, crucially, writing in Chinese characters. Many later court families traced their origins to such immigrants. The once-popular theory that a horse-riding people conquered Japan from the continent is no longer accepted by most scholars; the evidence points instead to gradual transfer through contact and migration.

Religion in the Kofun period centred on the worship of ancestors and of kami dwelling in mountains, rocks, islands and the sea. Bronze mirrors, jewels (magatama) and swords – the objects later known as the imperial regalia – were placed in tombs and used in rituals. Mount Miwa in the Nara Basin was worshipped as the body of a kami, and on the island of Okinoshima, between Kyushu and the peninsula, rituals for safe voyages left tens of thousands of offerings from the fourth to the ninth century.

The tombs themselves were sacred spaces. Haniwa – clay cylinders and later figures of houses, warriors, horses, shamans and animals – lined their slopes, separating the world of the dead from that of the living. Buddhism, arriving from Baekje in the mid-sixth century, would gradually replace the mound as the focus of elite religious display.

Haniwa are the best-known art of the period. Starting as simple cylinders, they grew into lively sculptures: armoured warriors, women in ceremonial dress, saddled horses, boats and houses, many now in the Tokyo National Museum. Bronze mirrors, both imported and locally cast, carried designs of deities and beasts, and the triangular-rimmed mirrors found in early tombs are central to the debate over Himiko's gifts from China.

In Kyushu, above all in present-day Kumamoto and Fukuoka prefectures, the sixth century saw decorated tombs (sōshoku kofun) whose chamber walls were painted with concentric circles, triangles, boats and horses in red, black and yellow – a regional art form distinct from the Kinai.

Many of the largest mounds are designated imperial tombs (ryōbo) managed by the Imperial Household Agency, which restricts access and excavation. They can be seen only from outside, while many regional tombs are open as parks.

The Kofun period established the Yamato kingship from which the later imperial house claims unbroken descent, and it fixed the Kinai as Japan's political core for centuries. The mirror, jewel and sword of its tombs survive as symbols of imperial legitimacy.

Its history remains politically sensitive. Because the major mounds are treated as imperial mausolea, systematic excavation has been limited, and several official attributions to named emperors rest on later tradition rather than evidence. Historians therefore increasingly use neutral site names such as Daisen Kofun instead of 'Tomb of Emperor Nintoku'.