In the Doctor Who episode s09e11 Heaven Sent,

If everything resets to its initial state on a regular basis, why didn’t the block of azbantium (the stuff that was 400x harder than diamond) reset as well, and prevent the Doctor from digging through?


4 Answers 4


The Doctor was only meant to visit this room once.

Room 12 has a markedly different appearance to the rest of the castle – in particular, the unusually smooth walls and large block of azbantium. This is the “final” room.

The castle is designed to get the Doctor to reveal the identity of the Hybrid. The designers thought he would only arrive in the trap room once, realise it’s impossible to escape, give up and tell the secret. I don’t think they anticipated the Doctor chipping away at the wall over billions of years.

If he’s only supposed to visit this room once, then there’s no need for the room to reset.

Sloppy on the designer’s part? A bit. But since this room connects to the outside world (and is apparently the only room to do so), maybe the rules are a bit different here.

In an interview with Steven Moffat in Doctor Who Magazine #495, the contents of which have helpfully been posted on Reddit, Moffat answers this exact question:

Why did the diamond wall not reset each time like the rest of the castle?

Because it's not a room in the castle, it's the outer wall of the dial. The clue is that it's 20 feet of Harder Than Diamond. Why bother making it so hard, if a resetting stone wall would do? This is the wall between his recycling puzzle box and freedom. They made it tougher than any living thing could ever get through. Except, of course, the Doctor.

I think the gist of it (this room is a bit special and now part of the castle proper) lines up with what I’ve written above.

  • 6
    The question that really bugged me - why do none of the Doctors think to take a blunt object (such as one of the spades) into Room 12? Using a tool has got to be easier (certainly less painful) than punching a wall repeatedly for billions of years... Commented Nov 29, 2015 at 0:40
  • 8
    @TheGiantofLannister He only seems to have a few minutes in Room 12 before the Veil arrives. I don’t think he realises that it’s a diamond wall until he’s in the room himself – at which point he doesn’t have time to go back for a spade.
    – alexwlchan
    Commented Nov 29, 2015 at 8:43
  • 5
    Now that I think about it, there are a whole lot of things in the castle that don't reset. His discarded clothes remain in the room where he left them to dry on the previous loop. The word "BIRD" that he traces in the dust remains in the teleporter room. And his skull(s) remain all over the castle. So all of these changes must be exempt from the "resetting," however it works.
    – Nathan K.
    Commented Nov 29, 2015 at 21:25
  • 8
    @NathanK.: The thing that gets me is that the first Doctor to get wet must have remained naked for the remainder of his iteration :P Commented Nov 30, 2015 at 0:03
  • 2
    @NathanK. The word bird is written as his last act before he effectively dissolves into sand. He writes it just before his new self steps out so the room doesn't have time to reset.
    – MrDobilina
    Commented Dec 8, 2015 at 14:45

The rooms only reset when he reenters them, and they only reset to when he "arrives" each time. So every time he goes back to the teleporter room from the azbantium room, there's no chance for the diamond to reset, and it carries over to the next cycle in its current state. Similarly, the word "bird" and the clothing. The skulls are outside of the castle, so they stay.


Well, the purpose of the confession dial was to get him to confess, not to imprison him. Therefore, I believe the diamond-thing didn't reset because the designer wanted to give the doctor a way out that would take a long time to get to.

  • I disagree. The designer wanted him to face despair, not to escape. So close and yet so thoroughly and humiliatingly out of reach: "no Doctor: there is no escape". There were not counting on him having the sheer willpower to escape anyway. Commented Dec 1, 2015 at 6:08

I agree. The rooms only reset to when he arrives each time but resetting of objects in the rooms is only limited to the objects that were there before he got there or when he arrived. So if he left his clothes to dry in the room, the clothes did not disappear or reset because they were not supposed to be there anyway. Same goes for the skull which was not there when the Doctor first came to castle, so they stayed. As for the writing in the sand left by the previous copy of the doctor, it may be that the doctor activated the transporter to make a copy of him and it had nothing to do with resetting of that room. Resetting of the room was just that.i.e., resetting of objects and not the copying of the doctor. Do not confuse the transporter making a copy of doctor with resetting of rooms. These were 2 different events. The diamond wall didn't reset back because it was the last room in the castle where the doctor was supposed to break and give up the truth about the Hybrid. Thats where his journey would end, he would confess and would be let free. Obviously this didn't happen and the doctor took advantage of this weakness in the design of room 12. The designer or what we can say with some degree of certainty, the Time lord president did not anticipate that the doctor will chisel away the diamond wall in a very very long time and thus he designed the wall not to reset. Of course it was a very big gamble on doctor's part. What if the diamond wall would also reset. That would have meant he would have to rethink his strategy in every cycle and leave a different message for the new doctor instead of ‘BIRD’.

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