Patroclus was responsible for Achilles' rejoining the battle of the Trojan War, at first by proxy and then for revenge. While Achilles was still refusing to fight for the Greeks, he let his friend Patroclus wear his armor and lead his troops. The Trojans, who thought Patroclus was Achilles, killed him. To avenge the death of Patroclus, Achilles rejoined the battle.
The Trojan Horse was a device conjured by Odysseus to get the Greek troops inside the Trojan Walls. The Trojans took the horse as a gift not knowing it was filled with warriors. After the Trojans welcomed the gift into their city, they celebrated what they thought was the departure of the Greeks, but while they slept, the Greeks poured forth from the horse's belly and destroyed Troy.