The Taira clan (平氏, Taira-shi) had chosen Ichi-no-Tani (一ノ谷, Ichi-no-Tani) well. The fortress sat on a narrow strip of land at Suma — the sea at its southern face, steep mountains rising to the north. Any attacker would have to come from the west along the coast, where the defenses were strongest, or cross the mountains — which the Taira considered impassable. They left the northern heights unguarded.

Minamoto no Yoshitsune (源義経, Minamoto no Yoshitsune) was twenty-five years old and had been fighting since adolescence. He had a gift — perhaps the most dangerous gift a commander can have — for seeing the battlefield from the enemy's perspective and then going exactly where the enemy had decided he couldn't. The unguarded cliff was not a weakness he discovered; it was a weakness he understood the Taira had created by being rational.

He divided his force. His older brother Minamoto no Noriyori (源範頼, Minamoto no Noriyori) took the main army west, where the Taira expected the attack. Yoshitsune peeled off with a detachment of somewhere between one hundred and one hundred fifty elite horsemen and climbed north into the mountains. According to some accounts — this may be a later literary embellishment — he first sent horses down the steep face of the cliff called Hiyodorigoe (鵯越, Hiyodorigoe), Bulbul-bird Pass, to test whether cavalry could make the descent. When the animals managed it, he committed his men to the same path.

They came down in darkness, in silence, reaching the floor of the Taira compound before dawn. Then Yoshitsune gave the order to fire the buildings.

For the Taira warriors waking inside, the sequence of events must have been nearly impossible to process. Noriyori was hammering the front gate from the west — that was expected, that was the battle they had prepared for. But these flames were behind them, inside their own walls, crackling up through the buildings where they ate and slept. The enemy had descended from a cliff they had decided was impassable. The tactical logic that had made Ichi-no-Tani feel safe now made it a trap. The sea was behind them and the mountains were apparently no protection at all.

The Taira broke. Senior commanders and common soldiers alike ran for the ships beached on the shore to the south. The Minamoto pursued them onto the beach, and the killing began in the shallows.

The most famous encounter of that beach happened between two men who should never have met. Kumagai Naozane (熊谷直実, Kumagai Naozane), a Minamoto warrior, spotted a figure in splendid armor swimming out toward the retreating Taira ships. He called out the samurai challenge: it was dishonorable to show your back to the enemy — return and face death properly. The swimmer turned around. That code of honor, bushi no michi (武士の道, bushi no michi), cost him his life.

Kumagai seized the man's reins and pulled off his helmet. He found himself looking at a young face — powdered in the court fashion, handsome, clearly a nobleman, the age of his own son. The young man was Taira no Atsumori (平敦盛, Taira no Atsumori), sixteen years old, a member of the Taira inner circle famous at court for his skill with the fue (笛, fue) — the Japanese flute. He had carried the instrument into battle, tucked inside his armor. Kumagai wept. Other Minamoto riders were approaching; if Kumagai didn't kill Atsumori, someone else would. He took the young man's head.

When Kumagai searched the body, he found the flute — the instrument called Saeda, an heirloom of the Taira clan. Everyone who saw it wept. The grief undid Kumagai completely. Within the year he shaved his head, took the Buddhist name Rensei (蓮生, Rensei), and became a priest. A warrior so broken by a single death that he surrendered the warrior life entirely.

The battle's larger consequences were immediate and decisive. Among the Taira dead at Ichi-no-Tani were senior commanders including Taira no Michimori, Tadanori, Tsunemasa, and young Atsumori himself. Taira no Shigehira was captured. The clan's hold on the Kinai region — the heartland of Japan centered on Kyoto — was broken. The survivors, perhaps three thousand men, fled east to Yashima (屋島, Yashima) on Shikoku, where they regrouped around the six-year-old Emperor Antoku (安徳天皇, Antoku Tennō) and the sacred imperial regalia they had taken from Kyoto.

Yoshitsune had not eliminated the Taira. He had cracked them open. They would rally at Yashima, fall at Yashima the following year, and be annihilated in the naval battle of Dan-no-ura (壇ノ浦の戦い, Dan-no-ura no Tatakai) in April 1185. But all of it traces back to the moment a young general stood at the top of a cliff that everyone agreed was impassable and thought: then that is where I will go.