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Radiocarbon dating is a very important tool in determining the age of ancient, often excavated, objects. However, the atmospheric ¹⁴14 concentration fluctuates. Therefore, radiocarbon ages must be calibrated using such data as tree ring, so that the estimated date is more reliable. Despite numerous adjustment efforts, there was a doubt about the validity of available calibration curve of ¹⁴C ages in particular between the 1st and 4th century in Japan. That was the period where a number of rice-cultivating small entities were integrated into a country with a central political power, which is symbolized by huge kofun-graves.

Source : Nihon Kodaishi Network

(*) The woods in Japan which cover this period (BC100 - AD400) were mostly Japanese cypresses which were found buried on the riverbed of Toyama-gawa, a tributary river of Tenryu-gawa. They were buried by landslide caused by the earthquake in 714.

(**) As for possible dates for Makimuku and Hashihaka related relics, two alternatives are indicated on this table: for Makimuku either AD220 - 260 or AD290 - 340 and for Hashihaka AD 240 - AD260 or AD290 - 340. The researcher who made this table says, the possibility of the early fourth century is higher and this corresponds to the traditional view about the building time of Hashihaka.

Last year, a new calibration curve IntCal20 was adopted, whereby the data from Japanese tree rings were employed a lot. The outcome might give a big change in the discussions about whereabouts of Yamatai.

As for the location of Yamatai, there were two opposing opinions for decades, the one supports North-Kyushu and the other Kinki. As I explained in a previous essay, Himiko, Queen of Yamatai, should have lived in the first half of the third century in Yamatai and died in 248, according to the official history of Wei Dynasty of China.

The possible site for Yamatai in Kinki area is Makimuku, and Hashihaka-Kofun is assumed to be the tomb of Himiko. However, Makimuku and Hashihaka were, according to the conventional understanding of the dating of yayoi potteries and kofun tombs, at earliest from the fourth century. There is a gap from the time when Himiko lived.

Since the radiocarbon dating was made available, many researchers, including those belonging to the National Museum of Japanese History, came to assume the age of the building of Hashihaka to be in the middle of the third century and the relics of the Makimuku ruins in the late second century or early third century. Together with other findings such as shift of excavated mirrors from North Kyushu to Kansai in the late second century and early third century, Yamatai-in-Kinki theory seems to have gained ground.

IntCal20 was issued in August 2020 and according to the new curve, there is more room to interpret that Hashihaka was built in the fourth century and Makimuku ruins were not substantially earlier. This means, Himiko was not able to live in Makimuku and be buried in Hashihaka.

I do not know what is being discussed among researchers. I am eager to know what discussions would come out from the new situation brought about by this latest technological input.