Most ancient battles were but parts of large-scale wars that ultimately decided the fates of kingdoms and empires.
Hence the popular quote, "We may have lost the battle, but not the war". However, history remembers instances where a single battle was so grandiose that it led to the complete collapse of entire empires and even civilizations.
The most epic of these are listed below.
The Sicilian Expedition - 415 - 413 BC
The Peloponnesian War was one of the bloodiest and most extensive conflicts in Antiquity. During the struggle that continued for more than 30 years, Sparta and Athens fought over dominance of Greece. Athens sent an expedition of 200 ships and 10 000 soldiers, the bulk of their army, to conquer Sparta's loyal ally - the Sicilian city of Syracuse.
Near the walls of the ancient polis, the Athenians were completely decimated in a battle that lasted for 3 days. After this defeat, Athens not only lost the war, they lost their glory. It never recovered and soon became part of other kingdoms and empires.
The Battle of Zama - 202 BC
The Battle of Zama marked the end of the Second Punic War and of the centuries-long rule of the Carthaginian Empire. The Roman general won the battle with a clever trick. He handed out whistles to his light infantry, which they blew and thereby scared the elephants in the army of the great general Hannibal.
The frightened animals trampled the Carthaginian army in their flight, with the Roman legionnaires finishing off the rest. At the end of the day, 20 000 Carthaginians lay dead in the battlefield near Zama, with another 20 000 captured and sold into slavery. Several years later, Carthage became a Roman province.
The Battle of Mobei - 119 BC
The Battle of Mobei put an end to the centuries-long conflict between China and the vast nomadic Xiongnu empire, which ruled over a significant part of Asia. Because of the constant attacks by the nomads, the Chinese built the Great Wall of China, although it was still not enough to stop the Xiongnu. After the fall of the Qin dynasty and resulting civil war in China, the danger of the Xiongnu increased several-fold.
The new emperor, first of the Han dynasty, decided to stop the invaders once and for all. The bloody battle that ensued in 119 BC in the Gobi desert was one of the largest in ancient history. 300 000 Chinese stood against 150 000 Xiongnu. The number of casualties was spine-chilling. The Chinese lost more than half their army but the Xiongnu lost all of theirs. In the aftermath of the destruction, the Xiongnu empire was no more.