How was Troy destroyed?

In ancient Greek mythology a long and bitter war took place between the Greeks—or Achaeans as they were also known—and the Trojans. It all started because Helen, the wife of King Menelaus of Sparta, fell in love with the Trojan prince Paris, and ran off with him. She had been bewitched by the goddess of love, Aphrodite, who had been chosen by Paris as the most beautiful of all the goddesses. Menealaus felt that his honor as king had been violated by his wife's desertion, and he and the other Greek kings set off to Troy with their armies to avenge the insult and get Helen back.
Largely because of constant interference by the gods, the Trojan War dragged on for ten long years, during which time the Achaeans lay siege to the city of Troy. The deadlock was finally broken when the Achaeans hit upon the brilliant idea of offering the Trojans the gift of a wooden horse in which a number of their troops were hiding. The Trojans foolishly accepted the gift, and once the Greeks were inside the city walls they set about slaughtering everyone in sight, sparing only a handful of women and children, who were subsequently sold into slavery.