house of cards

noun3

1. •
   A structure made by stacking playing cards in a pyramidal fashion.
2. •
   (figurative) A structure, argument, or arrangement that is inherently flimsy or fragile and thus might collapse if any adversity were to come along and challenge it.
3. •
   [before a noun] Any structure with alternating vertical and horizontal layers.

   • Dolmens impress only by their massiveness: their house-of-cards construction is the simplest possible […] — 1977