Smothered Mate in Xiangqi: The Cannon's 闷宫 Checkmate

What 闷宫 means, and how it differs from chess

闷 means stuffy or shut in, the feeling of a room with no air, and 宫 is the palace. So the name reads as the smothered palace: a General with nowhere to breathe.

Chess players will think of the smothered mate delivered by a knight against a king hemmed in by its own pieces. The spirit is the same, but the mechanics are not. In Xiangqi the usual finisher is the Cannon, and the Cannon's screen rule is what makes it work. The Advisor that is supposed to protect the General becomes the platform the Cannon fires over.

Definitions vary a little. Chinese teaching lists usually keep 闷宫 narrow, meaning a single Cannon against a General on its home point that is boxed in by a back-rank Advisor and a centre Advisor. A broader term, 闷杀, covers any mate where the defender's own pieces block the General, often after a sacrifice lures them into place. Some English sites split things the same way, with a smothered cannon checkmate and a wider smothered checkmate that includes Chariots and Soldiers. This article sticks to the classic Cannon version.

The classic shape

Put Black's General on its home point, with one Black Advisor in the palace centre and the other on the back corner on Red's right. Black's left Elephant can stay at home. Red has a Cannon on Black's side of the river, on the rank nearest the river, standing on the file of Black's right-hand Horse, and that file is empty all the way to Black's back rank. The Red General is on its home point. Red to move.

The Cannon drops straight down to the back rank, onto the point where Black's Horse started. Between the Cannon and the General there is now exactly one piece, the corner Advisor, so it is check along the back rank, and it is checkmate. XiangqiPlay's rules engine finds no legal reply for Black.

Why nothing helps

Walk through Black's options, because each one fails for a reason worth remembering. The General cannot step forward, since its own Advisor sits in the palace centre. It cannot step onto the right back corner, since the other Advisor is there. It can physically step to the left back corner, but that point is on the same back rank, still behind the same single screen, so the Cannon checks it there too.

The Advisors are no help either. The corner Advisor's only move is into the palace centre, which is occupied, so the screen cannot step away. The centre Advisor can move, but none of its moves lands on the back rank between the Cannon and the General. The one empty point there, the right Elephant's starting point next to the corner Advisor, is where a blocking piece would have to go, and nothing Black has can reach it.

Now imagine a Chariot on the Cannon's point instead. Its check along the back rank would be blocked by the corner Advisor. The Cannon needs that Advisor, which is the lovely irony of this mate: the piece placed to defend the General is the one that makes the check possible.

Setting it up in a game

Defenders move an Advisor into the palace centre all the time, because from there it guards both front corners against Horses. Once that has happened and the other Advisor is still on its back corner, the General's home point becomes a cage waiting for a Cannon.

What you need is a route to the back rank on the corner Advisor's side. That means a file where Black's Horse has left its starting point, or at least a back-rank point beyond the Advisor where your Cannon can land with no second piece in the way. A Cannon standing on the file of the enemy Horse, with a clear run to the back rank, is then one move from the drop.

The threat also works as a lever. If the smother is on, the defender has to spend moves stopping it, and those are moves not spent against your Chariots and Horses.

Everything mirrors, of course. With the Advisors the other way round, the corner Advisor on Red's left, the Cannon drops onto the left side of Black's back rank and the same logic holds.

How Black gets air

Take the same position, but move Black's Elephant from its home point to the middle of the palace's front edge, and replay the Cannon drop. It is still check, but now the Elephant can drop back to the back rank on the other side, onto the point beside the corner Advisor. With two pieces between the Cannon and the General, the check disappears. It is Black's only legal reply, and it is enough.

The second defence is an empty palace centre. Suppose the centre Advisor had been on the palace's front-left corner instead, with Black's central Soldier still on its starting point. After the same Cannon drop, the General can step up into the palace centre, and the corner Advisor can also step up there, taking the screen away. Either move ends the check.

The third defence is plain prevention. Keep a piece on the back-rank point next to the corner Advisor for as long as an enemy Cannon can reach that file, or keep a Chariot on the back rank where it can capture a Cannon that lands there.

Mistakes on both sides

Attackers usually miss this mate because they think of the Cannon as a piece that wants open lines. Against a boxed-in General, it wants a crowded line with exactly one piece in it.

The other attacking mistake is dropping the Cannon when a second piece stands between it and the General. Count the pieces on the back rank between the Cannon and the General before you move: one piece means check, two means nothing at all.

Defenders go wrong by tidying up. Bringing an Advisor to the palace centre is a good habit against Horses, but it is only safe if the General keeps a flight point or the back-rank line stays covered. Each time you move an Advisor, look along your back rank from the side, the way a Cannon would.

Make it a reflex

Once you have seen the smothered palace a few times, you will spot it from across the board. Repetition gets you there: XiangqiPlay's free puzzle library holds 5,000 engine-proven mate puzzles, and with a free account you can play the computer at any of its eight levels (Easy to God) and aim your Cannons at a crowded back rank.