The Silence is a religious order or movement. Their core belief is that silence will fall when the question is asked

Prisoner Zero says that the Pandorica will open and silence will fall.

River Song says that she will next meet the Doctor when the Pandorica opens.

The Doctor and Rory hear the silence.

An unknown voice says “Silence will fall”.

Abigail’s Song is themed around silence.

A Silent. Madame Kovarian and others wear the eye patches so they can remember the Silence.
The universe is cracked, the Pandorica will open and silence will fall
The crack was a powerful explosion happening across time and space. The crack first appeared in The Eleventh Hour on Amys bedroom wall.

A crack appears on Amys wall, eventually it opens up wide enough to allow Prisoner Zero to escape

The same shape as the crack appears on the TARDIS screen at the end of the Eleventh Hour

The crack in time appears on the Starship UK

The crack appears in World War II behind the TARDIS as it leaves

The Doctor and Amy notice the same crack as seen in Amy’s bedroom wall

Rory gets removed from time, only the Doctor remembers him.

The crack appears as Amy finds her Engagement Ring from Rory

The crack appears on the TARDIS screen as an unknown voice says “Silence will fall”
Some were tiny, some were as big as the sky. Through some we saw worlds and people, and through others we saw silence, and the end of all things.
The mysterious ‘Eye Patch Lady’ turned out to be Madame Kovarian. Under orders from the Silents she kidnapped Amy Pond and then stole her baby. The Silents wanted the baby to become a weapon to eventually destroy the Doctor.

“No, I think shes just dreaming”

“It’s fine, you’re doing it fine, just stay calm”

Madame Kovarian appears breifly in The Rebel Flesh

Well dear. You’re ready to pop aren’t you. Little one’s on its way.

Madame Kovarian is hoping to raise Amy and Rory’s child to be used as a weapon in a war against the Doctor.

Madame Kovarian is captured by River Song and is eventually killed by the Silents.
And now they’ve taken a child. The child of your best friends, and they’re going to turn her into a weapon just to bring you down. And all this, my love, in fear of you.
Clues and other references to the Silence, the Pandorica or other notes of interest.

Amelia clearly hears the TARDIS when she couldn’t have.

A persons shadow is seen inside Amelia’s house, was it Prisoner Zero or something else?

Amy doesn’t remember the Daleks. The music that follows the crack in time can be heard.

The (future) Doctor explains to Amy that she has to remember something that he told her when she was 7 years old.

The Doctor explains that time can be rewritten, no one remembers the Cyberking, Amy doesn’t remember the Daleks. There are no ducks.

26.06.10 – Amy’s time.

The Doctor finds a piece of the Tardis in the crack.

The Pandorica is a prison designed to keep the Doctor away from the TARDIS. The alliance believe he is the person that causes an explosion that will destroy the universe.
The only water in the forest is the river