The Persian Empire's military machine was powerful and ponderous. When Darius finally came to meet him, Alexander was already in southern Turkey. The situation for the Greeks was serious. They were still in the mountains, trying to find a safe passage to the sea. Darius managed to get in between and Alexander had to fight his way through.
30,000 Greeks faced 100,000 Persians across a small river called the Pinarus, near the town of Issus. Fighting across a river is always difficult, for the attacker has to wade through the water and climb the opposite bank before ever engaging the defender.
Parmenio led the Greek left and had a hard fight of it. Alexander personally led the right, which held the Macedonian cavalry. The battle was still very much at issue when Alexander led a charge straight at Darius himself.
Seeing Alexander cutting his way through the Persians, obviously making for the king himself, Darius panicked and fled. Once the king was seen abandoning the field -- he was easy to spot in his golden chariot -- the Persian army collapsed.
Issus marked the beginning of the end of Persian power in the Mediterranean. After Issus, Alexander knew he could bring Darius down; he began to dream of replacing him as King of Kings.
