His followers said he could walk on water. They said fish leaped into his hands at a word. Amakusa Shiro — born Tokisada, son of a Christian retainer — was no older than sixteen when he became the voice of a rebellion that would shake the Tokugawa shogunate to its foundations and change the shape of Japan for the next two hundred years.

The rebellion had been building for years. The Shimabara Peninsula and Amakusa Islands were governed by lords who taxed their peasants past endurance and persecuted Christians with a fervor the shogunate encouraged. When the uprising finally ignited in December 1637, it drew together Christian peasants and 鎌倉 (Kamakura)-era resentments, desperate farmers and masterless samurai — 浪人 (ronin) — who had been left without purpose since the great wars ended. They gathered behind the boy messiah.

For twenty-seven days the rebel force had besieged Shimabara Castle without breaking through. Then, sometime around January 8, 1638, they made a decision that transformed a losing siege into a masterstroke of defensive strategy: they abandoned Shimabara and marched south through the winter dark.

原城 (Hara-jo) — Hara Castle — sat on a promontory on the 島原半島 (Shimabara Hantō), Shimabara Peninsula, in what is now Nagasaki Prefecture. Sea cliffs on three sides dropped directly into the water. The only land approach was a strip of tidal marsh less than a half-mile wide that the ocean swallowed twice a day. The rebels dismantled their own boats and used the timber to patch the crumbling walls. Then 37,000 people — roughly 13,000 fighters among them, the rest women, children, elderly — hunkered down and waited.

The shogunate's response was overwhelming on paper: over 125,000 troops, the largest military mobilization since the Battle of 関ヶ原 (Sekigahara). Their first commander, Itakura Shigemasa, launched an early assault and was killed. His replacement, Matsudaira Nobutsuna, was a subtler man — but subtlety was no help when the geography made the castle nearly unassailable.

Week after week, the professional army of Japan's most powerful government could not break through a ruin defended by peasants and unemployed swordsmen. The siege stretched into weeks. Then months.

In desperation, the shogunate turned to the Dutch. The Protestant merchants at 平戸 (Hirado), had no love for the Catholic missionaries whose faith animated the rebels. More importantly, they had a powerful motivation to stay on good terms with the Tokugawa: theirs was the only Western trading relationship Japan still permitted. The Dutch captain Nicolas Couckebacker sailed the warship de Ryp into range and opened fire for fifteen days.

The guns overshot. Cannonballs fell in the shogunate's own camp. From behind the walls, the rebels composed mocking letters and sent them out to the besiegers: Were there no longer any courageous soldiers left in Japan? Were they not ashamed to call in foreign help against starving farmers?

The castle finally fell in April 1638 — not to military prowess, but to starvation. When the shogunate's forces stormed the walls on April 12–15, they found defenders so weakened they could barely lift their weapons. The killing that followed was total. An estimated 37,000 rebels and civilians were executed. Amakusa Shiro, still a teenager, was beheaded. His severed head was put on display in Nagasaki, where the Portuguese traders who might have mourned him were already being packed onto ships and expelled from Japan forever.

The boy who was said to walk on water never got the chance to try.