1. What Was Written on the Back of a 1,300-Year-Old Register
A single old paper fragment is registered in the national database. It is part of a household register from the Chikuzen province (around present-day Fukuoka Prefecture), created in 702. It is considered one of the oldest surviving household registers in Japan and is designated as an Important Cultural Property. [3]
If you turn this paper over, you find something completely different written on it. It is part of a ledger related to sutra copying from 748. This happened 46 years after the household register was made. The register’s preservation period had passed, and the sutra copying office used the back of the paper. [3]
This means the household register survived not because it was "carefully stored," but because it was a piece of paper whose back was used. Why did the sutra copying office use paper that government offices had finished with?
2. Why the Sutra Copying Office Used Expired Government Paper
The reason is that paper was precious at the time. The sutra copying office received expired official documents from other offices and used their backs for ledgers and other records. It is explained that household registers and census records survive to this day because of this use of the reverse side. [2]
The sutra copying office was a government office responsible for projects like copying sutras at Todai-ji Temple. The collection of documents made there and passed down to the Shosoin treasure house is called the "Shosoin documents." These include records of sutra copying, temple construction, and Buddha statue making, as well as household registers and census records written on the backs. [1]
According to the National Diet Library, the Shosoin documents make up most of the Nara period documents that exist today. [1] The number of items varies by source, with estimates of "over 10,000" or "over 10,000," but it is about 10,000 items. It is considered rare globally for so many 8th-century documents to remain. The backs of papers that had finished their duty became a rare collection of historical sources. Who were the people writing on these backs, and what was their daily life?
3. "Stomachache" as a Reason for Leave: Records of Workers
In the sutra copying office documents, reasons for leave include stomachaches, the death of a parent, caring for a child, family rituals, and washing work clothes. There are also records of wages and work amounts, giving a glimpse into the lives of Nara period officials. [2] It is interesting that on the back of a national household register, there are these daily records of working people.
However, the sources consulted for this article could not confirm when or why these ledgers were placed in the Shosoin. While the reason for using them as backing paper is known, the process of how they entered the storehouse remains unclear. What is known is the result: they were passed down for over a thousand years. What environment were the papers placed in after entering the storehouse?
4. Did the "Breathing" of the Storehouse Protect the Documents?
You may have heard that the wooden walls of the Shosoin storehouse expand and contract with humidity, opening and closing gaps to regulate moisture. This is called the "Azekura breathing theory" and was widely known from the Meiji to early Showa periods. [4]
However, a paper by staff of the Shosoin Office states that it was confirmed that the wood of the Azekura storehouse does not actually shrink or expand (Nagata, 1984). [4]
There is another easily overlooked point. The North and South storehouses are Azekura-style, but the Middle storehouse is considered to be of plank construction. [4] The documents are currently stored in the Middle storehouse. [5] This means the room for the documents is not an Azekura wall to begin with. Explaining why the documents survived by the breathing of the Azekura walls does not fit this fact. (This is an arrangement based on cross-referencing materials.) So, what protected the inside of the storehouse?
5. Wooden Storehouses and Chests Slow Humidity Changes
Actual measurements show that the temperature and humidity inside the Shosoin storehouse vary less and more gently than the outside air. Inside the wooden chests (called *kara-bitsu*) that hold treasures, the variation is even smaller, with humidity ranging from 60–70% throughout the year. [4] Note that this 60–70% figure is for inside the *kara-bitsu*, not the storehouse itself.
The paper concludes that the moisture-regulating function of the cypress storehouse and the *kara-bitsu*, many of which are made of cedar, act as a double buffer wall, maintaining a stable humidity environment. [4] Think of it like putting a coat over a sweater in winter; the outer cold is harder to feel. Similarly, the double wooden walls weakened the outside humidity fluctuations. However, this is just an analogy; in reality, the wood regulates humidity.
The building is raised off the ground, with a height of 2.7 m (about 9 feet) under the floor. [4] There are currently 206 *kara-bitsu* remaining, 168 of which are from the Nara period. [4] However, these are containers for treasures; it is not known which containers the documents were in.
6. People Who Ventilated and Repaired the Roof
Even with the system of storehouses and chests, the treasures can deteriorate if left unattended. At the Shosoin, *bakuryo* (airing out treasures to prevent insects) has been conducted since the Nara period. The records of this, called "Bakuryo-shi ge" in five volumes, are also passed down as treasures. [4] Until the Edo period, it was irregular, but it has been conducted every year since 1883. [4]
The buildings were also maintained. In 1254, lightning struck the door of the North storehouse directly. Firefighting prevented major damage, and repairs were made afterward. In recent years, there was a complete dismantling and repair in 1913, and roof re-thatching and partial reinforcement between 2011 and 2014. [4] The Middle storehouse came under imperial seal from the Heian period onward. [4]
The staff member who compiled this paper states that the treasures have been passed down for about 1,300 years due to the storehouse environment and the efforts of people who maintained it. They note that human involvement in preservation has not changed since the Nara period. [4] However, the paper’s subject is treasures in general, not just documents.
7. The Difficult Problem of Organization After Protection
The documents protected in the storehouse underwent organization by the Historiographical Institute at the University of Tokyo from the Meiji period to the mid-Showa period. They are now housed in the Middle storehouse as 667 volumes and 5 books. [5]
However, during the organization process, there was a task to select official documents like household registers and census records from the paper backs first. As a result, the connected records were largely separated, creating many fragments with unknown origins. [5] From the perspective of the household registers, they are precious treasures. But from the perspective of the ledgers, the continuity was cut. It seems there are different difficulties in protecting items and deciphering their contents.
8. If You Want to Try Investigating Yourself
What you can do today: Get one used printout and write today’s date and a word on the back. Later, turn it over and line up the dates on the front and back to see which was written first. For paper with a ledger on the back of a household register, you can consider the order of writing by comparing the dates.
If you want to read the sources: The question "When and why did the ledgers enter the storehouse?" was not answered in this article. Takahata Makoto’s "Document Preservation and Environmental Maintenance at the Shosoin" in the National Museum of Ethnology research reports details the actual measurements of temperature and humidity and the history of airing out. The introduction to the "Shosoin Document Catalogue 1" by the Historiographical Institute at the University of Tokyo is a clue to understanding the organization process.