How a Swamp Became Tokyo: The Untold Story of Edo

How a Swamp Became Tokyo: The Untold Story of Edo

In 1590, a man on horseback arrived at the edge of a vast marshland on the Kantō Plain. The air smelled of salt and river mud. Reeds stood taller than men. The only settlement was a scattering of thatched roofs near the mouth of a bay — a fishing village called Edo, a name that simply meant “entrance to the bay.”

The man was Tokugawa Ieyasu. Other warlords might have seen this place as exile. He saw something else entirely.

Within a single generation, the swamp would begin to vanish. Within a century, the city that replaced it would be the largest on Earth — bigger than London, bigger than Paris, bigger than anything the world had seen before.

This is the story of how that happened.

💡 This article explores the history behind our sleep story episode. Watch on YouTube: Tokyo — A City Born from Swampland

Table of Contents

Open Table of Contents

The Hostage Who Learned to Wait

To understand how Tokyo was built, you first need to understand the man who built it — and the decades of patience that shaped him.

Tokugawa Ieyasu was born in 1543 at Okazaki Castle in modern-day Aichi Prefecture, as Matsudaira Takechiyo. His family controlled a small domain caught between two powerful clans — the Imagawa to the east and the Oda to the west. Around the age of five, his father sent him as a political hostage to the Imagawa clan to secure an alliance. But the boy never arrived. He was intercepted by the Oda clan and held captive for roughly two years.

Eventually returned to the Imagawa, the young Ieyasu spent the next decade at their capital in Sumpu — modern-day Shizuoka — learning military strategy, administration, and, above all, the art of waiting. He was not mistreated, but he was not free.

His chance came in 1560. Imagawa Yoshimoto, the clan leader, was killed in a surprise attack by Oda Nobunaga at the Battle of Okehazama. With his captor dead, the seventeen-year-old Ieyasu returned to Okazaki Castle and began to assert his independence — cautiously at first, then formally allying with Nobunaga in 1562.

What followed were thirty years of alliances, betrayals, and calculated survival. While Oda Nobunaga conquered central Japan and Toyotomi Hideyoshi unified the rest, Ieyasu watched, waited, and grew stronger. He fought when he had to. He allied when it served him. And he never moved before the time was right.

This patience — not the kind a person chooses, but the kind that settles into bone — would define everything he built.

Why Edo? Hideyoshi’s Gambit

By 1590, Toyotomi Hideyoshi had united Japan. The last major holdout, the Hōjō clan, fell after the Siege of Odawara. Their vast territories in the Kantō region — eight provinces stretching across the eastern plains — were now empty of a lord.

Hideyoshi offered them to Ieyasu. In exchange, Ieyasu would surrender his five provinces in central Japan, including the lands around Okazaki that his family had held for generations.

Was this a reward or a punishment? Historians still disagree. The Kantō provinces were larger in total land value, but they were far from Kyoto, the political heart of Japan. By accepting, Ieyasu would gain territory but lose proximity to power. Refusing, however, would have meant war with Hideyoshi — a war Ieyasu could not yet win.

He accepted without complaint. In August 1590, he rode into Edo with his retainers and looked out across the marshland, the tidal flats, and the grey haze hanging above the bay.

Where others saw mud, Ieyasu saw geometry. A low hill, just high enough for a castle. A wide bay, deep enough for ships. Rivers running outward like the veins in the back of a hand. And marshland that could serve as a natural moat — a defense the land had already made.

He chose Edo as his capital and began to build.

Sekigahara: The Battle That Changed Everything

When Hideyoshi died in 1598, the fragile unity he had imposed began to fracture. Two factions formed among Japan’s most powerful lords — those loyal to Hideyoshi’s young son, led by Ishida Mitsunari, and those who saw opportunity in the power vacuum, led by Ieyasu.

On October 21, 1600, the two sides met on a narrow plain near the village of Sekigahara in central Honshū. Approximately 160,000 warriors faced each other in fog and rain. The battle lasted roughly six hours. When it was over, Ieyasu’s Eastern Army had won a decisive victory — partly through military skill, partly through the defection of key Western Army commanders whom Ieyasu had quietly courted beforehand.

Three years later, in 1603, Emperor Go-Yōzei formally appointed Ieyasu as shōgun — the supreme military ruler of Japan. He established his government not in Kyoto, where shōguns had traditionally ruled, but in Edo.

The swamp was about to become a capital.

Draining the Swamp

The Edo that Ieyasu inherited was barely a town. To transform it into a seat of power, he launched one of the most ambitious civil engineering projects in pre-modern history.

The first problem was water. The Hibiya Inlet — a shallow tidal bay — extended almost to the base of the hill where the castle would stand, making expansion impossible. In the 1590s and into the early 1600s, workers began filling this inlet with earth, creating dry land for samurai residences and commercial districts. The soil came from an unlikely source: Kanda Hill, a plateau to the north of the castle site, was systematically cut down and carried south to fill the wetlands.

The excavated hillside became the Kanda River, rerouted to serve as both a water supply and a transport channel. Other canals followed — the Dōsan-bori connecting the castle to Edo Bay for construction materials, the Onagi channel for food and salt. Inner moats spiraled outward from the castle in concentric rings, with the innermost circuit spanning roughly five kilometers and the outer moat extending sixteen.

Edo Castle itself rose over decades, with major construction lasting from 1603 to 1639. At its peak, the main keep — completed in 1638 — rose over 40 meters tall across five stories, making it one of the largest castle towers in Japan. It would stand for less than twenty years before the Meireki Fire of 1657 reduced it to ash. It was never rebuilt. Ieyasu did not build it alone. Under a system called tenka bushin, regional lords across Japan were ordered to contribute labor and materials in proportion to their income, turning the castle’s construction into a nationwide project.

Tens of thousands of workers whose names were never recorded carried earth on their backs, drove wooden stakes into soft ground, and dug channels through marshland. They did not know what they were building. But piece by piece, a city was taking shape.

Five Roads, One Nation

Ieyasu understood that a capital is only as strong as the roads that connect it to the rest of the country. From Nihonbashi — a wooden bridge first built in 1603, the same year he became shōgun — five great highways radiated outward like fingers reaching across Japan.

These were the Gokaidō, the Five Highways. The Tōkaidō ran southwest along the coast to Kyoto with 53 posting stations. The Nakasendō took an inland route through the mountains to the same destination. The Nikkō Kaidō led north to the sacred shrines at Nikkō. The Ōshū Kaidō pushed further northeast into the provinces of Mutsu. The Kōshū Kaidō headed west into the mountains of Kai — modern-day Yamanashi.

Along these roads, posting towns sprang up — wooden inns, tea houses, stables. Travelers could find a hot meal, a warm bath, and a bed for the night. The roads carried more than people. Seeds, stories, recipes, songs, and dialects moved along them, slowly stitching a fragmented country back together.

But the highways served another purpose — one that was purely political. In 1635, the third shōgun, Tokugawa Iemitsu, formalized a system called sankin-kōtai, or alternate attendance. Every regional lord in Japan was required to spend alternating years in Edo, maintaining a residence in the capital at all times. Their wives and children remained permanently in Edo — not officially hostages, but not free to leave either.

The system was brilliantly effective. The constant travel and dual residences consumed a significant share of a lord’s income — by some accounts, the majority of a domain’s total expenditures — leaving little surplus for building armies. The roads that connected the nation also drained its warlords.

Ieyasu, the former hostage, had turned the entire country into something he understood intimately: a system where proximity to power was both a privilege and a chain.

The Swamp That Became the World

By the late seventeenth century — barely a hundred years after Ieyasu had first ridden into the marshland — Edo’s population had surpassed one million. London at that time held roughly 600,000 people. Paris was smaller still. No city on Earth had ever gathered so many lives in one place.

The village at the entrance to the bay was gone. In its place stood a city of wood, water, and candlelight held in paper — a city whose canals and bridges rivaled those of any European capital, whose culture was about to enter one of the most creative periods in human history.

But that is a story for another article.

For now, stand at the edge of the Imperial Palace moat in central Tokyo. The water is dark and still. The stones along its banks were placed there over four hundred years ago by hands that left no names. A heron stands at the water’s edge, motionless, watching the reflection of a city that grew from mud.

The moat remembers what the skyscrapers forget.

It all began in a swamp.

FAQ

When was Tokyo founded? Tokyo as a city name dates from 1868, when the Meiji government renamed Edo as the new imperial capital. However, Edo’s history as a major settlement began in 1590, when Tokugawa Ieyasu established it as his base of power.

Why did Tokugawa Ieyasu choose Edo? Ieyasu was transferred to the Kantō region by Toyotomi Hideyoshi in 1590. He chose Edo specifically for its geographic advantages — a defensible hill for a castle, a deep bay for maritime access, and rivers that could serve as natural moats and transport routes.

How big was Edo compared to European cities? By the late 1600s, Edo had over one million residents, making it the largest city in the world. London had roughly 600,000 residents around 1700 and did not reach one million until around 1800. Paris reached that figure even later, in the early nineteenth century.

What were the Five Highways of Edo? The Gokaidō were five major roads radiating from Nihonbashi bridge in Edo: the Tōkaidō (to Kyoto via the coast), the Nakasendō (to Kyoto via the mountains), the Nikkō Kaidō (to Nikkō), the Ōshū Kaidō (to the northeast), and the Kōshū Kaidō (to Kai province, modern Yamanashi).

What is sankin-kōtai? Sankin-kōtai (alternate attendance) was a system formalized in 1635 requiring all regional lords to spend alternating years in Edo. Their families remained in the capital permanently. The system maintained political control by keeping lords financially strained and physically separated from their home territories.

Sources