In J.R.R. Tolkien's legendarium, Gondolin is a secret city of Elves in the First Age of Middle-earth, and the greatest of their cities in Beleriand. The story of the Fall of Gondolin tells of the arrival there of Tuor, a prince of Men; of the betrayal of the city to the dark Lord Morgoth by the king's nephew, Maeglin; and of its subsequent siege and catastrophic destruction by Morgoth's armies. It also relates the flight of the fugitives to the Havens of Sirion, the wedding of Tuor and the Elf Idril, and the childhood of their son Eärendil.
Scholars have noted the presence of tank-like iron fighting machines in Morgoth's army in early versions of the story, written soon after Tolkien returned from the Battle of the Somme. They have likened the story of the Fall of Gondolin to the sack of Troy in ancient Greek literature, or to Virgil's Aeneid; the role of Tuor's wife Idril has similarly been compared to that of Cassandra or Helen of Troy in accounts of the Trojan War.