Atrium is played on a 5×5 board with the following starting setup:
Each turn players one of theiror one orthogonal step. Blocking units are pushed out of the way, if there is a free square for them to move into.
After moving the following checks are made:
winline- if you have an orthogonal or diagonal 3-in-a-row of all three units of a single type, you win!
loseline- otherwise, if you happened to create such a line for your opponent, you lose!