Two characters on a stone by the entrance of office blocks, schools and apartment buildings. You have passed hundreds. Behind many of them is a sealed metal box of newspapers, drawings and name lists that nobody opens until the building comes down.
定礎 teisoHow to read the dateA walk of seven plaquesFacts checked October 2026
You have been up the Tokyo Metropolitan Government towers for the free view, and you have walked out of Shinjuku Station (新宿駅) past more office lobbies than you could count. At shin or chest height beside a good share of those doors is a rectangle of polished stone with two large characters and a line of small ones. English dictionaries give it one line: "cornerstone". Japanese people mostly walk past it too. This piece teaches you to read it, tells you what is sealed behind it, and gives you a short walk where seven of them are confirmed.
Why spend an hour on wall plaques instead of another observation deck? Because this is the one piece of writing on a Japanese building that tells you its age, and with about ten kanji you can read every one in the country. What you give up: there is nothing to enter and no ticket. The interesting part is inside the wall and you will not see it.
What the two characters say定礎 · teiso
定 (tei) means to set or fix. 礎 (so) is a foundation stone, the block a pillar stands on. Together, teiso is the act of setting the foundation stone, and the ceremony for it is the teiso-shiki (定礎式). The plaque itself is a teiso-ban (定礎板).
The name is older than the practice it now describes. In a steel and concrete building the foundation goes in first and there is no single stone to set, so the ceremony drifted from the start of the job to the end. Japanese explainers on the subject agree on the result: the date on a modern plaque is normally the month the building was completed, not the month it was begun. Older plaques may carry the start date instead.
Nothing requires any of this. The Building Standards Act says nothing about teiso, and plenty of buildings have none. Where one exists, it is usually near the main entrance or on the south-east side. Granite and marble are the common materials; bronze and stainless steel also turn up, and some are cast into the wall itself.
The date line on the Shinjuku Park Tower plaque. Three of its eight characters repeat on every plaque in Japan: 年, 月 and, most of the time, 吉日.
Reading the date年 · 月 · 吉日
The small line follows one pattern: era name, year number, 年, month number, 月, and often 吉日. That last pair, kichijitsu, means "an auspicious day". It is the standard way of not naming the day at all, so a plaque ending in 吉日 gives you a month and nothing finer.
The era is two characters, and for buildings you will meet only five. Add the number in the figure below to the year on the stone and you have the Western year. If the year is written 元 instead of a numeral, that is year 1 of the era. Numerals are often the kanji ones, built the way you would say them: 十 is ten, so 十二 is 12 and 四十七 is 47. A plaque reading 昭和四十七年三月吉日 is March 1972.
Newer plaques sometimes switch to Arabic numerals, add the Western year, or drop the era completely. One more trap applies to old buildings: before the war, horizontal Japanese on signs was normally written right to left. If a plaque seems to say 礎定, read it from the other end.
Japanese write-ups say the big characters are sometimes cut from the owner's own handwriting. One collector-reported case: the entrance plaque of the manga publisher Leed (リイド社) in Kōenji uses the brushwork and signature of Saitō Takao, the author of Golgo 13.
Bar widths are to scale. Shōwa ran 63 years, longer than any other block, so 昭和 is the era worth memorising first.
What is behind the stone定礎箱 · teiso-bako
On many buildings the plaque is a lid. A cavity is left in the wall or a column, a box called a teiso-bako (定礎箱) goes in, and the plaque is fixed over it. The box is usually copper or stainless steel so that it will not rot; older ones can be lead or wood. What goes in is up to the owner and the builder. The usual list is the building's drawings, lists of the people involved, the newspapers of the day of the ceremony, and coins in circulation that year. Some hold a talisman from the local shrine or a company history.
It is opened once, at demolition. That is how the few known contents became known.
Roppongi, sealed 1971, opened 2012. When IBM Japan's former head office was cleared for redevelopment, the plaque was taken off after 41 years. Inside: daily papers, an English-language paper and a construction trade paper; design drawings; a recruitment brochure; a brochure for the new building; completion photographs; and two brass plates of names, one Japanese, one English.
Sendai, sealed 1965, opened 2023. The city took the box out of its old city hall and put all ten items on display that winter: the inner plate, a summary of the construction, lists of officials, council seating, committee members and site-office staff, the budget and contract record, an organisation chart, the newspaper of 4 August 1965, and the city newsletter of 1 August.
Hongō, sealed 1890, found 2014. Workers breaking up the brick foundations of the University of Tokyo's old library hit a metal box about 10 by 17 centimetres. It held a metal plate wrapped in the government gazette of 25 August 1890. The front named the building; the back named the engineers, which is how the university learned who had designed it, Kuru Masamichi, with Yamaguchi Hanroku supervising. The original records had been lost.
The stone you can touch is a few centimetres thick. Everything of interest sits just behind it and stays there for the life of the building.
Where the custom came from定礎式 · teiso-shiki
The short answer in Japanese explainers is that the cornerstone ceremony is a European practice with Greek and Roman roots, and that it reached Japan with brick and stone construction in the Meiji period. Every version of that sentence is hedged with "it is thought that". No source found for this article names a first Japanese teiso ceremony or a first plaque.
The University of Tokyo's own notice on the 1890 box is the most telling evidence. It compares the box to a munafuda, the wooden tag nailed inside the roof of a temple or shrine to record its builders, and to a modern teiso-bako, and says no comparable Meiji example was known. So in 1890 someone was already sealing names into a foundation, but how that became a polished stone by every door is not established here. Treat anyone who gives you a neat origin date with caution.
Seven plaques in Nishi-Shinjuku西新宿 · 代々木
The stretch between the Metropolitan Government complex and the south side of Shinjuku Station is lined with towers from the bubble years and just after, and seven of their plaques, all dated between 1989 and 1999, were photographed and posted to Wikimedia Commons in 2024. The inscriptions below are read from those photographs. Between them they cover every variant in this article: kanji numerals, Arabic numerals, 吉日, 元年, a Western year, and a designer's rewrite.
#
Building
Carved
Reads as
1
Tokyo Metropolitan Assembly Building (都議会議事堂)
平成二年十二月
December 1990. Running-script 定礎 cut deep into pale granite. No 吉日.
2
Shinjuku Park Tower (新宿パークタワー)
平成六年四月吉日
April 1994. Pink-flecked granite, black-filled letters.
3
Tokyo Opera City (東京オペラシティ)
平成11年3月
March 1999. Arabic numerals inside an era date.
4
Nichigas head office, built for Enix (代々木4-31-8)
竣工 1996年8月
"Completed August 1996". 定礎 redrawn in thin rounded lines on metal, with client, designer and builder listed below.
5
Bunka Gakuen University (文化学園大学)
平成十年二月吉日
February 1998. A cast metal plate set in black stone.
6
Aioi Nissay Dowa Shinjuku Building (代々木3-25-3)
平成元年3月 · 1989
March 1989. 元 marks year 1, two months into the new era.
7
Shinjuku Takashimaya, Times Square (新宿高島屋)
平成八年十月吉日
October 1996. White stone, low on the wall.
Stop 4 is the one collectors talk about. A 2017 Daily Portal Z piece on "designer teiso" calls it a stealth plaque: the lettering is so faint that from the wrong angle the wall looks blank. The client named on it is Enix, the game company behind Dragon Quest.
Getting there: Tochōmae Station (都庁前駅) on the Ōedo Line for stop 1; the walk ends at Shinjuku Station (新宿駅), south side. Hatsudai Station (初台駅) is beside stop 3 if you want to cut it short.
When: Daylight, any day. Weekends are quieter around office entrances. Raking morning or late-afternoon light makes shallow carving easier to read and photograph.
Reality check: The sources confirm that each plaque exists and what it says. None says which wall it is on. Start at the main entrance and work along the base of the building.
If you have circled a building twice, ask the guard at the door: 定礎はどこにありますか (teiso wa doko ni arimasu ka).
If a guard comes over while you are crouched at a wall: 定礎を見ているだけです (teiso o mite iru dake desu).
Before you photograph a plaque inside a doorway or lobby: 写真を撮ってもいいですか (shashin o totte mo ii desu ka).
Out along the north side of Kōshū Kaidō, back along the south side. The road is the border between Shinjuku and Shibuya wards, so the walk crosses it twice.
The honest part
You cannot see inside, and you never will. The box is opened when the building is demolished, by the owner, and what comes out is shown publicly only when the owner feels like it. Sendai's display ran for six weeks in a city hall lobby.
Many plaques have no box at all. Sources say a box is "often" fitted, and nothing on the outside tells you which kind you are looking at. A plaque can be a lid or just a label.
This walk is seven small rectangles on the walls of 1990s buildings. Nothing on it is old. Pre-war plaques exist, and the right-to-left rule above is for them, but no specific surviving one could be confirmed from published sources for this piece, in Marunouchi, Nihonbashi or anywhere else, so none is named.
The seven here were photographed in early 2024. Buildings get re-clad, hoarded off and sold. If one is missing, that is information too: the collectors' grail, a plaque dated 昭和六十四年, exists because Shōwa 64 lasted seven days in January 1989. The Daily Portal Z writer knew of only two in Tokyo in 2017, the best known in Itabashi, and gave no address.
Walking distances and times below are map estimates, not measured on foot.
If you only have one hour
A weekend morning, when the light is low and the lobbies are empty. As written it takes about 75 minutes; the last line tells you what to cut.
Tochōmae Station. Cross to the Metropolitan Assembly Building, which faces the Government towers across the plaza. Find 平成二年十二月 and do the sum: 2 + 1988.
Walk south to Shinjuku Park Tower. This is the plaque in the first figure; read all eight characters without looking at your phone.
West along Kōshū Kaidō to Tokyo Opera City. Note the Arabic 11 and 3.
Cross the road and go south to the Nichigas building at Yoyogi 4-31-8. Move your head until the lettering appears.
Back to Kōshū Kaidō and east along the south side to Bunka Gakuen University, then the Aioi Nissay Dowa building a block or so on. Find 元.
Shinjuku Takashimaya, Times Square. Last plaque, then Shinjuku Station.
Running late? Drop stop 4 and stay on the main road; that brings the walk to about an hour. Keep stop 1. After that, the test is the next building you pass on your own: stop, find the stone, and read the year.