Comment by NooneAtAll3

theoretically there's a design for "indestructible" fortress (rhoburb, you are a genius)

1) fill corner board with pieces 2) cover the border (from inside) with pawns 3) cover the promotion square on the border with the king

king can't exit the board, pawns can't walk backward to leave space, filler doesn't allow these 2 to make way

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the real holy grail that will never be achieved I fear