Tarnin Austa
From Tolkien Gateway
Tarnin Austa, or Gates of Summer, was a great feast held in Gondolin on the first day of summer. It was custom to begin a solemn ceremony at midnight, continuing it until dawn of Tarnin Austa. No-one could speak from midnight to daybreak, but upon the rising of the sun they would burst into ancient songs, with choirs standing upon the eastern wall. At that time the city was filled with silver lamps, and lights of jeweled colors hung on the branches of the new-leaved trees.
It was upon this usually cheerful and festive morning that Morgoth's armies attacked Gondolin, beginning the (in)famous Fall of Gondolin.
