thumb|The fall of Turgon's Tower. Illustration by [[Tom Loback<!--recognised Tolkien artist-->, 2007 ]]
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.
City
Founding
thumb|upright=1.75|Sketch map of [[Beleriand in the First Age. Gondolin (centre top) is encircled by mountains. ]]
The city of Gondolin in Beleriand, in the extreme northwest of Middle-earth, is founded with divine inspiration. The mightiest of the Elvish cities, it is hidden by mountains and endures for centuries before being betrayed and destroyed. in the First Age. According to The Silmarillion, the Vala Ulmo, the Lord of Waters, shows Turgon the Vale of Tumladen in a dream. Thus guided, Turgon travels from his kingdom in Nevrast and finds it. Within the Encircling Mountains is a round level plain surrounded by sheer walls; a ravine and tunnel, the Hidden Way, lead out to the southwest. In the middle of the vale is the steep Amon Gwareth, the "Hill of Watch". There Turgon decides to found a city, designed like the Noldor Elves' former city of Tirion in Valinor. Gondolin is built in secret. The Hidden Way is protected by seven gates, all constantly guarded; the first of wood, then stone, bronze, iron, silver, gold, and steel. After it is completed, he brings all his people from Nevrast to dwell in the hidden city—almost a third of the Noldor of Fingolfin's House—and nearly three quarters of the northern Sindar.
|author = J.R.R. Tolkien
|source = The Hobbit
|width = 40%
|align = right
Gondolin develops its own Sindarin dialect, containing regional elements and words adapted from another Elvish language, Quenya.