but a deep underlying shift in the history of gondolin separates the earlier and later accounts : for whereas in the last tales ( and later ) gondolin was only discovered after the battle of unnumbered tears when the host of turgon retreated southwards down sirion , in the silmarillion it had been found by turgon of nevrast more than four hundred years before ( 442years before tuor came to gondolin in the fell winter after the fall of nargothrond in the year 495 of the sun ) .