The Historical Context of Kofun Construction

Here is a summary of the chronology of kofun construction.

Year or Period	Description	Imperial Reign per Nihon Shoki	Imperial Reign per Kojiki
57	The King of Na (Wa no Na no Kuni) receives a gold seal from Emperor Guangwu of the Later Han Dynasty
c. 2nd century	Construction of a large settlement begins at Makimuku, eventually leading to the building of kofun	Emperor Keikō (12) Emperor Seimu (13)	Emperor Kaika (9) Emperor Sujin (10)
238 or 239	Himiko sends envoys to Wei and receives the title '親魏倭王(Shin-Gi-Wa-Ō: Pro-Wei Queen of Wa)'	Empress Regent Jingū	Emperor Sujin (10)
Mid-3rd century	Construction of Hashihaka Kofun	Empress Regent Jingū	Emperor Sujin (10) Emperor Suinin (11)
391 - 404	Wa-Koguryo War	Emperor Nintoku (16) Emperor Richū (17)	Emperor Ōjin (15) Emperor Nintoku (16)
Early 5th century	Construction of Daisen-ryō Kofun (designated as Emperor Nintoku's tomb)	Emperor Richū (17) Emperor Hanzei (18) Emperor Ingyō (19)
527	Iwai Rebellion	Emperor Keitai (26)
538	Buddhism introduced from Baekje	Emperor Senka (28)
Mid-6th century	Construction of Ozuka Kofun	Emperor Kinmei (29)
593	Prince Shōtoku becomes regent	Empress Suiko (33)
645	Isshi Incident	Empress Kogyoku (35)	―
663	Battle of Baekgang	Prince NakanoŌe = Emperor Tenji (38)
672	Jinshin Rebellion	Emperor Kōbun (39) Emperor Tenmu (40)
694	The capital was moved to Fujiwara-kyo.	Empress Jitō (41)
Fujiwara -kyō Period	Construction of Takamatsuzuka Kofun	Empress Jitō (41) or Emperor Mommu (42)
710	Capital relocated to Heijō-kyō	Emperor Genmei (43)

In the early Kofun period, the first giant kofun, Hashihaka Kofun, was built at the foot of Mount Miwa(Makimuku). Numerous kofun exist in Sakurai City, Nara Prefecture, with Hashihaka Kofun serving as their icon.

Subsequently, when the capital was moved to Naniwa Takatsu Palace, the kofun construction area shifted to Kawachi(Osaka Prefecture). The tomb of Emperor Nintoku, Japan's largest kofun, is extremely famous and represents the Mozu-Furuichi Kofun Group World Heritage Site.

I was taught to call it Emperor Nintoku's tomb, but there are many possible names such as Daisen Kofun, Daisen Kofun, and Daisen-ryō Kofun. The textbook terminology has changed over time for various reasons.

Various events occurred within the timeframe from the construction of Ōzuka Kofun to the construction of Takamatsuzuka Kofun. The Asuka period falls entirely within that timeframe. Takamatsuzuka Kofun was built during the terminal phase of the Kofun period.

Various debates exist regarding the construction period and the buried person of Hashihaka Kofun.

The Imperial Household Agency has designated the person buried in Hashihaka Kofun as 迹迹日百襲姫命 (Yamatototohi-momosohime-no-mikoto). Momosohime was a daughter of the 7th Emperor Kōrei (7) and served to convey divine will to Emperor Sujin (10). She was a woman with shamanistic characteristics, and according to the Nihon Shoki, she became the wife of the deity Ōmononushi. However, it is somewhat unnatural that her tomb is larger than Emperor Sujin's tomb.

Some researchers believe that the person buried there is Himiko*. This theory has existed since the Taisho period (1912-1926), and it appears that Himiko is identified with Momoso-hime. In other words, this would mean that Yamatai-koku equals the Yamato Kingdom. Since Himiko is said to have died in 248 CE, it's understandable why such theories exist.
*Note for those unfamiliar with Himiko: She was the queen of Yamatai-koku as described in the Wei Zhi (Chronicles of Wei).

However, the reliability of the Wei Zhi itself is questioned, and since excavation surveys cannot be conducted at the Hashihaka Kofun, there is a lack of decisive evidence and things remain unclear. Amid this situation, the Hashihaka Kofun has been attracting renewed attention in recent years due to the start of investigations using elementary particles that can penetrate matter.
→ Tumulus × Space (Nara History, Art and Culture Village)