I need ways to build a VERY solid wall (History project, build your own castle)?

Question

So far I have

4 foot thick concreate wall with titanium renforcements. Plated with 6" of Iridium. The Iridium has diamond powder mixed into it and is covered in Plasma Nitride + Iron Ball paint. On the back of the wall there is another 6" of plasma nitrided, lead lined titanium. So, prettey much inpenatrble right? WRONG! Need to harden the walls a LITTLE more for perfection.

So, any takers?

PS: It needs to be able to survive a white hot missle, plummeting down from space at 27 times the speed of sound.

Answer 1

how about the same, but scaled up 20 times?