On 29 July 1014 Basil II destroyed Samuel's army in the Kleidion pass by sending a force over the mountain onto its rear. The mass blinding that followed is the most famous atrocity in Byzantine history — and it is reported by a chronicler writing fifty-five years later.
By 1014 Basil II had been at war with Samuel of Bulgaria for most of thirty years, and had learned how to fight him: not by seeking a decisive battle, but by taking fortresses one at a time, campaigning every year, and refusing to be drawn into the mountains on Bulgarian terms.
That summer Samuel tried to stop him at Kleidion, a narrow point in the valley of the Struma between the Belasica and Ograzhden ranges, by blocking the pass with a palisade and holding it in strength. Basil's frontal attacks failed.
The battle was decided by a flank march. Nikephoros Xiphias took a detachment over the shoulder of Mount Belasica and came down behind the Bulgarian position on 29 July, and the army in the pass broke between the two forces.
The First Bulgarian Empire had been beaten once already, by John Tzimiskes in 971, and had recovered under a new leadership in the west — Samuel and his brothers, the sons of a provincial governor, who rebuilt a Bulgarian state around Ohrid while Basil II was fighting civil wars at home.
Basil's early attempt to deal with them ended in humiliation at Trajan's Gate in 986, where his army was ambushed in a pass and he escaped with difficulty. It is the defeat that shaped his later method.
From about 1000 he campaigned in Bulgaria every year with a professional army and a system: reduce the fortresses, garrison them, come back next spring. It was slow, expensive, and it worked, and by 1014 Samuel was defending a shrinking territory against an opponent who no longer made mistakes.
Samuel fortified the pass at Kleidion — the name means "the key" — with a wooden palisade and a strong force, and for several days the Byzantine assaults were beaten back with heavy loss.
Basil then detached Nikephoros Xiphias, the strategos of Philippopolis, with orders to work round the position. Xiphias took his men over the steep ground of Mount Belasica and descended behind the Bulgarian line on 29 July.
Attacked front and rear in a confined valley, the Bulgarian army disintegrated. Samuel escaped only because his son Gabriel Radomir got him out; the rest of the army was killed or taken, and the sources put the prisoners in the region of fourteen or fifteen thousand.
The story everyone knows is this: Basil had the prisoners blinded, ninety-nine men in every hundred, leaving one in each hundred with a single eye to guide the rest home; Samuel saw the column arrive at Prilep, collapsed, and died two days later.
It needs stating plainly where that comes from. The account is in John Skylitzes, who wrote around 1070 — about fifty-five years after the battle — and it is not in the contemporary or near-contemporary material. Yahya of Antioch, writing much closer to the events, does not describe it.
Modern historians divide on it. Some accept a mass blinding on a smaller scale, since blinding was a routine Byzantine punishment and the mutilation of prisoners is well attested elsewhere; others regard the numbers and the arithmetic of one guide per hundred as a literary construction. What can be said is that Samuel did die on 6 October 1014, and that the story was firmly established in the Byzantine tradition within two generations. This archive reports it as what Skylitzes wrote, because that is what it is.
It did not end the war. This is the point most popular accounts get wrong, and it matters for judging both men.
Samuel died in October 1014 and was succeeded by his son Gabriel Radomir, who was murdered by his cousin Ivan Vladislav, who fought on and died besieging Dyrrhachium in 1018. Only then did the Bulgarian nobility come to terms, and the annexation was completed that year — four years after the battle.
Basil spent those four years doing what he had done for the previous fourteen: taking fortresses, accepting surrenders, and campaigning every season. Kleidion destroyed the Bulgarian field army and, in the chronicle tradition, killed its ruler. The state it belonged to took four more years to finish.
The annexation of 1018 ended three and a half centuries of Bulgarian independence and put the Byzantine frontier back on the Danube for the first time since the seventh century. It is the high-water mark of the medieval empire.
It is also the source of Basil's posthumous name. He was called Boulgaroktonos, the Bulgar-slayer, but not by his contemporaries: the epithet appears about a century and a half after his death, when the empire had lost the Balkans again and needed the memory of the emperor who had held them.
For Bulgaria the battle became something else entirely — a national memory of catastrophe and endurance, commemorated in modern monuments, and the reason the Belasica pass is a place of pilgrimage rather than a footnote.