The historical site of Thermopylae became a battlefield not only in the famous conflict of 480 BC. but several more times in history. In 996 AD the Bulgarians, under Tsar Samuel, taking advantage of the involvement of the emperor Vasilios Bulgaroktonos with the Arabs, besieged Thessaloniki. However, unable to capture the well-fortified city, they moved south and plundered as far as Larissa, which they razed to the ground, literally as far as Corinth.
The intensity of the Bulgarian invasion obliged the emperor to allocate forces to Greece, which he commanded under the general Nikephorus Uranos . As the Bulgarians moved northward again, laden with booty and dragging with them thousands of women and children they had captured, Uranus followed them carefully, striking, when possible, their rearguards.
This game of cat and mouse continued all the way to Thermopylae until the summer of 997 AD . There Uranus crossed the river with his army and found himself in front of the Bulgarians, who, due to loot and prisoners, were moving slowly. The Bulgarians camped on the south bank, facing the Byzantines.
Due to heavy rains the river was impassable and so the Bulgarians placed small garrisons along the bank they controlled. Unable to move, the two armies faced each other for a few days, giving a sense of security to the Bulgarians, who believed that the Byzantines could not cross the river.
However, the famous Tabrizi light horsemen of the Byzantine army discovered a point where the army could, with effort, pass. Immediately Nikephoros Uranos hastened to the spot and after making sure that the passage was possible he ordered the army to be ready to cross as soon as night fell.
So it happened. With absolute order the Byzantines crossed the river at night and approached the Bulgarian camp. However, they did not attack, waiting for dawn, for fear of killing the Greek prisoners of the Bulgarians in the darkness and confusion. Suddenly, as soon as he began to chant, the Byzantines with the chant "Lord Mercy", came forward.
The surprised Bulgarians were unable to resist, but those who could fled, leaving behind booty and prisoners. About 1,000 who tried to resist were killed. Another 12,000 were captured. But the most important thing was the release of the prisoners, who with tears in their eyes thanked the soldiers who saved them. Samuel and his son Radomir who were following him were saved. But this defeat was the beginning of the end of the First Bulgarian Empire.