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How to Read Date Inscriptions on Japanese Swords

Paul Martin



Before the implementation of the Gregorian calendar the Japanese used the lunisolar calendar. It wasn’t until the January 1, 1873 (Meiji 6), that Japan adopted the Gregorian solar calendar in order to bring themselves into alignment with the majority of the world. In order to do so, they had to skip almost a whole month. The day before  the 1st of January 1873 had been the second day of the 12th month, in the 5th year of Meiji. The western calendar equivalent of this would have been to go to bed on December 2, 1872, and the next day would have been January 1, 1873. This probably was not too difficult for the Japanese to deal with, as historically a leap month was added occasionally to ensure that the irregular months maintained alignment with the seasons.


This rather fluid disparity in Japanese and western dates should be taken into account when reading the archaic date inscriptions on the tangs of Japanese swords. The date of manufacture had often been inscribed on the tang (nakago) since at least the Kamakura period (1184-1332). However, it is important to remember that with swords dated prior to 1873, the numeric months do not necessarily correspond with the numerical order of the months of the Gregorian calendar. So, when translating or transliterating sword date inscriptions, it is best to read them as a numeric month rather than converting them into a Gregorian month. However, modern Japanese swords are still dated using the archaic writing system, but are in accordance with the numerical order of the months of the Gregorian calendar.


Reading the date inscriptions is mostly straightforward. However, a few tools makes the task a little easier. First, there are three basic types of archaic Japanese dating to be considered. These are:


    * Nengo: era names

    * Eto: the Chinese sexagenary calender (animal zodiac)

    * Koki (皇紀): the imperial calendar


Nengo and eto are commonly used and even sometimes used together. Koki is based upon the timeline of the imperial lineage since the legendary founding date of Japan (660 BCE) by the first emperor Jimmu. The Koki dating system was not implemented until 1873 and is frequently seen on swords made during the World War II. However, this dating system was abandoned after the war.


Historically, nengo (era names) were decided by court officials and did not necessarily relate directly to the names of the ruling emperor of that period. The era names changed frequently due to superstitions and religious beliefs. It wasn’t until the ascension of Emperor Meiji in 1868 that Japan adopted a single era name to the life of a ruling emperor.


Date inscriptions generally start with the name of the era, followed by the year of that era, and/or possibly the eto characters for that year. There are many eras, so the reading of the first two characters should be carefully researched to give you an approximation of the date. These are then followed by a number and the actual character for year (nen ), the numeric month of the year and the character for month (gatsu ), the numeric day of the month followed by the character for day (hi or jitsu ). Alternatively, instead of a specific day and month in the inscription, the characters for spring () or fall () are sometimes used instead. Other characters commonly used in date inscriptions in place of the numeric day of the month are the words for auspicious day: kichi jitsu (吉日) or kisshobi (吉祥日).


Below is a chart of the basic numbers used for days and months. There are some variations of some of the characters. In the case of the number four (), it is pronounced “shi.” This is the same sound for the pronunciation for the character , which means “death.” Similarly, the character for nine () can be pronounced “ku,” which also invokes the idea of “kurushii,” or extreme pain. Therefore, inscriptions containing these two characters are often avoided and alternative characters are used instead. For example, the character for four will almost always be written as two two’s.


The basic numbers and their variants:

1 2 3 4 5 6 7 8 9 10 20 100 1000
Ichi Ni San Shi



Go Roku




or Nana


Hachi Ku Ju Niju Hyaku Sen











The numbers are also used in combination to produce greater values. For example, 10 is expressed by the character “ju” (); for a value greater than 10 but less than 20 it is followed by another of the preceding numbers (example: 十一= 11, 十二=12, and so on). If a fundamental number precedes another character such as 10 (), 100 (), or 1,000 (), it multiplies that number (二十 = 2 x 10 20). Any other numbers following that equation are then added for the final amount (二十三 = 2 x 10 + 3 = 23).


The Chinese sexangenary calendar of 12 animals, known in Japanese as Eto, is also referred to as ju-ni-shi (十二支). The 12 animals are used in combination with 10 stems to create a 60-year cyclical calendar.


The 10 stems are:























The 12 animals are:





































Rabbit Dragon Snake Horse  



Monkey Rooster Dog Boar




There are also archaic names for the months that are rarely used, but can sometimes be seen in inscriptions, or on some sayagaki (inscriptions written on the surface of scabbards).


Old name Reading Meaning Standard characters Reading
睦月 Mutsuki First month 一月 Ichi-gatsu
如月 Kisaragi Second month 二月 Ni-gatsu
弥生 Yayoi Third Month 三月 San-gatsu
卯月 Uzuki Fourth Month 四月 Shi-gatsu
早月, 皐月




Fifth Month 五月 Go-gatsu
水無月 Minazuki Sixth Month 六月 Roku-Gatsu
文月 Fumizuki, Fuzuki Seventh Month 七月 Shichi-gatsu
葉月 Hazuki Eighth Month 八月 Hachi-gatsu
長月 Nagatsuki Ninth Month 九月 Ku-gatsu
神無月 Kannazuki, Kaminazuki Tenth Month 十月 Ju-gatsu


Shimotsuki Eleventh Month 十一月 Ju-ichi-gatsu
師走 Shiwasu Twelth Month 十二月 Ju-ni-gatsu
閏月 Uruuzuki, Jungetsu Leap Month*

*Sometimes an additional month was added to maintain alignment with the seasons.



Here are some examples of date inscriptions on the tangs of Japanese swords, and their translations.


Ex. 1.

Tenna (can also be read as Tenwa) ni nen ni gatsu hi: A day in the second year of Tenna era (1682).


Ex. 2.

Heisei Tsuchinoe-ne Kisaragi Kichi jitsu: An auspicious day in the second month of the year of the Rat (2008), in the reign of Emperor Heisei (Akihito).


Date inscription 3.

Koki ni sen roppyaku (roku + hyaku) nen ju ichi gatsu hi: A day in the 11th month of 2,600th year of the imperial reign (1940).


Using the information provided, try to read and translate the next three date inscriptions yourself. The correct answers will be given at the end of June’s article. Here is a link to a list of nengo to help you on your way.





Paul Martin is a former British Museum curator, and a Hyogiin (Trustee) for The Society for the Promotion of Japanese Sword Culture (NBSK). He is also a recognized specialist by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT).

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