The Trojan War started when Paris, Prince of Troy, either kidnapped or seduced Helen, Queen of Sparta, away from her husband Menelaus. Invoking an oath sworn by all the suitors of Helen to support her husband, Menelaus with his brother Agamemnon, King of Mycenae, as the commander gathered the Achaean Greeks to conquer Troy and recover his wife.
The first gathering of forces at Aulis did not go well. The Achaeans did not know the way to Troy and attacked the Kingdom of Mysia, ruled by Telephus. Achilles cut Telephus in the battle. Telephus’ wound could only be healed by the man that wounded him. Achilles at first refused claiming he knew nothing about medicine. Odysseus thought that the weapon that caused the wound could heal it. Bits of the spear were placed on the wound and it healed. Telephus told the Greeks how to get to Troy.
It took eight years after the first expedition was scattered by a storm to regroup back at Aulis. A fleet of more than one thousand ships was gathered at Aulis. It is here in the Iliad that Homer gives the famous Catalogue of Ships. There are 28 different kingdoms listed that sent ships and soldiers to the gathering. Totaled together there are 1,178 ships. These ships are called pentekontoroi because they were manned by fifty rowers. That puts the number of troops at just under 60,000 men.
After the 1,178 ships were gathered the winds stopped. The seer Calchas told the gathered Greek kings that the Goddess of the hunt, Artemis, was angry at Agamemnon because he had killed a sacred deer and also bragged he was a greater hunter that the Goddess. She refused to let the winds blow until Agamemnon sacrificed his daughter Iphigenia. At first the King of Mycenae refused, but the other leaders threatened to replace him with Palamedes as the commander of the expedition.
Agamemnon relented and agreed to sacrifice the girl. In different versions of the story, he either killed her, or replaced her with a deer to fool the Goddess, or Artemis took pity on the girl and at the last minute replaced her with a lamb and took the girl and made her a priestess.
In any case the wind began to blow and with the directions to Troy they had gotten from Telephus the Greeks set sail for Troy.