For centuries, there was no question about where Japan's center was. 京都 (Kyōto) was old, imperial, sacred — the city where emperors had lived for eight hundred years, the source of all official legitimacy, the place where a warlord had to go if he wanted to be seen as something more than a warlord. 江戸 (Edo) was a fishing settlement on a tidal flat in the east, surrounded by swamps, chosen by the Tokugawa clan as their seat for reasons that were, at the time, largely strategic: it was far from Kyoto, far from rival power centers, defensible, and expandable.

In the spring of 1603, Tokugawa 家康 (Ieyasu) received from Emperor 後陽成天皇 (Go-Yōzei Tennō) the title of 征夷大将軍 (Seii Taishōgun) — Barbarian-Subduing Generalissimo, the ancient title that conferred military authority over Japan. It was March 24, 1603. Ieyasu was sixty years old. He had been maneuvering toward this moment for most of his adult life.

Within weeks, a wooden bridge was completed in the heart of Edo over the 日本橋川 (Nihonbashi-gawa). Ieyasu named it 日本橋 (Nihonbashi) — Japan Bridge — and designated it the official starting point of the 五街道 (Gokaidō), the Five Highways: the 東海道 (Tōkaidō) running southwest to Kyoto and Osaka; the 中山道 (Nakasendō) cutting through the mountains to the same destination; the 奥州街道 (Ōshū Kaidō) running north into the deep provinces; the 日光街道 (Nikkō Kaidō) leading to the shrine complex that would later enshrine Ieyasu himself; and the 甲州街道 (Kōshū Kaidō) heading west toward the old Takeda heartland of Kai. Every 里 (ri) marker — one ri being approximately 3.93 kilometers — along every one of these roads would be measured outward from this bridge.

The name was political theater of the highest order. Japan didn't start at the imperial palace in Kyoto. It didn't start at any ancient sacred site or ancestral shrine. It started here, at a wooden bridge in a city that had barely existed a generation ago. The emperor still lived in Kyoto. The emperor would continue to live in Kyoto for another 265 years. But the center of the realm — the point from which all distances were measured, all processions calculated, all travel planned — was Edo.

The bridge became the busiest place in feudal Japan almost immediately. Fish markets crowded its approaches. Money changers and merchants set up houses along its banks. Woodblock prints from the Edo period — particularly those by 歌川広重 (Utagawa Hiroshige) and 葛飾北斎 (Katsushika Hokusai) — show 日本橋 (Nihonbashi) packed with travelers, 侍 (samurai) retinues, porters bent under loads, vendors selling food and paper. It was the Times Square of feudal Japan, the one place that everyone, eventually, passed through.

But the bridge's deepest function was political. When the 参勤交代 (sankin-kōtai) system was formalized in 1635, every 大名 (daimyō) in Japan was required to spend alternating years in Edo — maintaining a residence there, keeping his family there as de facto hostages, and traveling the Five Highways to and from his home domain every other year. These processions were vast, ceremonial, and deliberately ruinous: a middle-ranking daimyo might bring hundreds of armed retainers and servants, spending a fortune on travel, lodging, gifts, and the maintenance of his Edo residence. The cost was the point. Lords who spent their wealth on processions couldn't spend it on armies.

Every one of those processions began and ended at 日本橋 (Nihonbashi).

The wooden original burned in the Great 明暦 (Meireki) Fire of 1657, which destroyed more than half of Edo and killed an estimated 100,000 people. When the bridge was rebuilt, a small change was made: the original name had reportedly been written with the characters 二本橋 (Nihonbashi) — "two bridges" — and was now rewritten as 日本橋 (Nihonbashi), "Japan Bridge." Whether this was deliberate political restatement or incidental calligraphy is debated; the result was permanent.

In 1911, the Meiji government replaced the wooden bridge with the current stone and steel structure — Western engineering wearing Japanese ornamental detail, bronze dragons flanking the corners. In 1964, a concrete expressway was hastily built directly over it to handle traffic for the Tokyo Olympics, blocking the bridge's sky view for the first time in its history. That expressway is now being removed and relocated underground, in a project expected to finish around 2040. When it's done, 日本橋 (Nihonbashi) will see open sky again for the first time in eighty years.

A bronze plaque on the bridge today marks it as the "Road Distance Zero Point of Japan's National Highways" — 日本国道路元標 (Nihon Kokudō Roji Hyōjun). Different roads, different materials, different country entirely from the one Ieyasu built. But the distance is still measured from here. It has been measured from here for over four hundred years.

Ieyasu built his bridge in the same year he became shogun. The coincidence was not accidental. The shogunate was the political claim; the bridge was the geographic one. Together, they said the same thing: Japan begins here, in the east, in our city. Come and see.