Fortress deals the whole deck into ten visible columns. In this version, tableau cards may build upward or downward by rank, regardless of suit or color.
One card moves; only a king fills a space
Move an exposed card onto the next higher or lower rank. Runs cannot travel together, and kings and aces do not connect. An empty column accepts only a king. Four foundations build from ace through king by suit; there is no stock or reshuffle.
Use both rank directions to free a low card
A blocker may have a receiver above or below its rank. Compare which destination leaves the next move available, rather than taking the first legal one. Because a cleared column cannot receive an ordinary blocker, check the king’s route before relying on that future space.