Trojan War

The Trojan War, also known as the plural Trojan Wars, (TV: The Ark) was a conflict fought circa 1200 BC between the Greeks and the people of Troy. The war began when Paris, the son of King Priam of Troy, ran off with Helen, wife of King Menelaus of Sparta. The war ended after ten years, thanks to the First Doctor, who came up with the idea of using a wooden horse containing Greek soldiers. Believing the Greeks to have retreated, the Trojans brought the horse inside the walls, allowing the hidden Greeks to sack the city. (TV: The Myth Makers)

was also present at the Trojan War at some point in the conflict, extracting chemicals from the brains of humans. (TV: The Mark of the Rani)

Around 1885, Professor Odysseus James and Lady Emily Carstairs observed the Fall of Troy when their experiments on the Lamp of Chronos opened up a window into the past. (COMIC: Gaze of the Medusa)

Later references
One of the things that Mr Parsons taught his students about in their history class was the Trojan War. (TV: School Reunion)

By the time that humans left Earth on the Ark, the Trojan Wars were said to take place in the First Segment of Time. (TV: The Ark)

The Fourth Doctor recalled Troy while using K9 in the same way of a Trojan horse to reach the third planet, the hideout of the Shadow. (TV: The Armageddon Factor)