Board and setup
The board is 7 files (a to g) by 8 ranks, with a river between ranks 4 and 5. Each side has a 3 by 3 palace, but the two palaces sit in opposite corners: Red holds the bottom left (a1 to c3) and Black holds the top right (e6 to g8). The whole setup has 180 degree rotational symmetry.
Red moves first. This is open information: both players see the whole board and both reserves.
The pieces
The Chariot, Cannon, Horse, Elephant, Advisor, and General move as they do in xiangqi. The Soldier is the one standard piece with a changed move, and the Treasure is new. In the diagrams below, a green dot marks a quiet destination, a green ring marks a capture, and a red cross marks a point the piece cannot reach.
Chariot: slides any distance orthogonally, the strongest piece on the board. Here it can take the soldier on d7.
Cannon: moves like the Chariot on open lines, but captures only by jumping exactly one screen piece, friend or enemy. On the right, the cannon on d2 takes the chariot on d7 over its own soldier screen.
Horse: steps one point orthogonally, then one point diagonally outward. If the orthogonal step is occupied, that whole direction is blocked. On the right, the soldier on d5 takes away both forward destinations.
Elephant: moves exactly two points diagonally, is blocked by an occupied midpoint (the elephant eye), and can never cross the river.
Advisor: moves one point diagonally and stays inside the palace.
General: moves one point orthogonally and stays inside the palace. One xiangqi rule retires itself here: because the palaces sit in opposite corners, the two generals never share a file, so the facing-generals rule never comes into play.
Soldier: moves one point forward or sideways, never backward. Unlike a standard xiangqi soldier, it can move sideways from the opening move.
Treasure: the one new piece. It steps one point in any of the eight directions, is not confined to the palace, and never promotes. It is a flexible defender near the palace and an attacker after it advances or returns as a drop.
There are no promotions and no past-river changes. Soldiers move the same on both sides of the river; the river only stops the Elephant, which never crosses it.
Capture, hold, drop
When you capture any piece other than the General, it changes to your color and enters your reserve. Both reserves are open information, have no size limit, and keep pieces for as long as needed. On your turn, either move a piece on the board or drop one piece from your reserve onto an empty point. Generals are never captured or held in reserve.
Chariots, Horses, Cannons, Soldiers, and Treasures may drop on any empty point. Advisors and Elephants keep their normal territory restrictions.
A dropped piece is live immediately. A drop may give check or deliver checkmate, and a dropped Soldier can step sideways wherever it lands. The one limit is the usual one: no move, drop included, may leave your own general in check.
How games end
Checkmate wins. A player with no legal move also loses, even when not in check. There is no fifty-move or no-progress draw.
On the third occurrence of the same position, a player who gave check on every one of their moves in the repeating cycle loses. If neither player was the sole perpetual checker, the repetition is drawn.
Games can also end by timeout, resignation, or abandonment.
A sample game
This engine game shows both uses of the reserve: an Advisor returns to defend its palace, then Red finishes with a mating Soldier drop.
Play on Mistboard
Fortress Xiangqi is playable on Mistboard. Play against an engine or challenge a friend. No account required.