A wall is the stack of tiles each player builds in front of themselves before play starts — two tiles deep, nineteen tiles wide, so each wall holds 38 tiles. Push all four walls together and you get the "brick" everyone draws from as the hand plays out.
Building the wall is half muscle memory, half ritual: shuffle the tiles face-down, then each player stacks their own two-deep row. Once all four are pushed into a square, someone rolls the dice to decide where the wall breaks and dealing begins.
It's a small thing, but a wall that's built sloppy — gaps, uneven stacks — makes for an annoying game later, when a rushed hand knocks half of it over mid-Charleston. Take the extra ten seconds. Future you, three hands in, will thank you.
New to the table? Start with our step-by-step guide to American mahjong. Tile sets and mats are in the shop.