You have uncovered a Sign of the Gods (place 1 resource on the scenario reference card).
Flip this card back over.
Although this city-state was founded ages ago and stood for over a thousand years, it is no more. The tales tell of a single night in which Sarnath fell. Now very little of it remains: only a vast marsh where the city once stood tall and proud. Among the ruins you find no standing buildings, but rubble of marble, brick, and chalcedony. But as you approach the remains, lightning splits the sky. There is a blinding flash. As you blink your eyes, everything changes. Where before no city stood, now there looms a ghostly image of Sarnath as it once was. Near the lake, where the lightning struck, you find a curious and ancient idol of green stone. It is coated with seaweed and chiseled in the likeness of a great water lizard. One of the gods of this realm, perhaps?
Poszukiwania Kadath #131.