Tarnin Austa ( "Gates of Summer" or more literally "Passage into Summer") was a celebration held in the city of Gondolin on the first day of summer each year. 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 the elves 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.

(The Book of Lost Tales, Part Two.)