Reroute66

Reroute66 is inspired by Gerd Degens' Chess66, which adapts Chess to a board with a couple extra spaces that overlap with a4 and h5. In Reroute66, these new spaces are called A4 and H5, using the capital letters A and H for two new files with only one space apiece on them. Instead of simply jutting off the sides of the board, each new space pushes its rank over by half a space. From White's perspective, A4 pushes the 4th rank half a space right, and H5 pushes the 5th rank half a space left. By overlapping with a4 and h5, these spaces may be reached through vertical movement from other spaces on the board. Unlike Chess66, Reroute66 derives its rules simply from the geometry of the new board.

I chose the name Reroute66 to echo the name of the famous highway Route 66, to indicate that this was a revision or reworking of Chess66, and because rerouting of movement is an actual part of this game.

Setup

The most significant difference between this board and the 8x8 Chess board is its change in geometry. As each new space pushes its rank inward, the spaces in the middle two ranks become rhombus-shaped instead of square-shaped. While the spaces that were already part of the 8x8 board become right-leaning rhombuses, the two new spaces are left-leaning rhombuses. There are two places on the board where a pair of spaces overlap. The two overlapping spaces are a left-leaning rhombus and a right-leaning rhombus. This is illustrated on the board by using horizontal lines of alternating color in the area that these two spaces share. Since most rhombus-shaped spaces are right leaning, the vertical columns of spaces shift to the next file over between the 4th and 5th ranks. If you note the file label at the bottom and the file label at the top of the same column, you will see that they are different. For each column, the file markers at the bottom apply to ranks 1 to 4, and the file markers at the top apply to ranks 5 to 8. Aside from the two new spaces and the changes they make to the geometry, the one difference from the usual setup for Chess is that the Black Queen goes on e8, and the Black King goes on d8. This is to give each Queen the same access to the two new spaces.

The coordinates could have been designed so that the file of a column doesn't change, but this would be doable only by replacing some of the coordinates used in Chess with new coordinates, which would be less desirable than allowing the file to shift in a vertical column of spaces.

Pieces

Thanks to its new geometry, piece movement will be defined entirely in terms of geometric relations and not in terms of algebraic ranks and files. Nevertheless, the movement of each piece will be defined in a way that on the usual 8x8 Chess board, they would all move exactly as they do in Chess. The only difference from Chess will be that this board opens up new possibilties of movement from some positions. None of this is unprecedented, as other games with unusual topologies, such as Hexagonal Chess and Spherical Chess, have already done the same thing. I will introduce concepts as I describe the pieces, and I will address the pieces in an order that lets me introduce the most basic concepts first.

Rook

In Chess, the movement of a Rook could be described with either the word orthogonal or lateral. Orthogonal movement goes along a single dimension. For example, a1 to h1 goes along a single rank, and a1 to a8 goes along a single file. As the ranks and files are represented in algebraic notation, though, a Rook in this game may change both rank and file in a single move. So, I will just use the word lateral, which describes movement through the sides of spaces. Lateral movement in the same direction goes through the opposite sides of spaces. In this diagram, note that the Rook's vertical movement may take it to another file, as files are represented algebraically.

Each pair of overlapping spaces is known as a Switch. These two spaces share a side at one end, which they share with the same adjacent space. A4 and a4 both share a side with a3, and h5 and H5 both share a side with h6. So, from a1, a2, or a3, vertical movement is possible to either A4 or a4, and from there it may continue down either vertical column of laterally connected spaces. To illustrate, here is a movement diagram showing how the White Rook on a1 can move.

However, once the Rook is in the Switch, it no longer has the option of moving along either column. It can move vertically only in the column of laterally connected spaces it find itself in. To illustrate, this diagram shows where a Rook may move from a4.

Likewise, if a Rook is in one of the branches of a Switch, it can move vertically only along the column of laterally connected spaces it finds itself in. This is illustrated by this diagram for the Rook on a6:

Bishop

On the Chess board, diagonal movement always changes the algebraic rank and file in a uniform manner. But because of the shifting over of some spaces, it doesn't always work out that way in this game. For this game, diagonal movement is understood as movement between spaces that share a corner but no sides, and diagonal movement in the same direction continues through opposite corners of spaces. In this diagram for a Bishop on d4, note that it is legal for it to move to d5, because d4 and d5 are diagonally connected.

While diagonal movement in Chess is always colorbound, diagonal movement on the Route66 board can change color. From either A4 or H5, a Bishop has one path away on each color. So, by moving to A4 or H5 on one turn and moving away on another, a Bishop may change the color of the spaces it moves on. This can be seen in this diagram for a Bishop on A4:

Note that from a4 and h5, a Bishop can move away on only one color. The two new spaces, A4 and H5, are the only spaces on the board that connect diagonally to a space of each color. This is thanks to the corner that A4 shares with a4 and the corner that H5 shares with h5. Because of this shared corner, a4 and A4 are each diagonally adjacent to b3, for each shares a corner with it without sharing any sides with it. For the same reasons, h5 and H5 are each diagonally adjacent to g6.

Although A4 also shares a corner with b4, the diagram above shows that the Bishop on A4 cannot move to b4. To understand why, let's first note that movement from one space to the other must go from the interior of one to the interior of the other. Sides and corners shared with other spaces are borders, and movement from one space to another must cross a border, not start or stop on one. So, for two spaces to be diagonally adjacent, there must be a line of movement that passes from the interior of one to the interior of the other without passing through any sides of either space. But there is no such line between A4 and b4. Movement through the corner would have to turn about 90 degrees, which means there is no diagonal direction of movement connecting these two spaces. Additionally, a direct line from one to the other would run parallel with an already established lateral direction, and another space lies between them in that direction. So, they are not adjacent in this direction, and it is not a diagonal direction. So, despite sharing a corner, they are not diagonally or laterally adjacent to each other, and there is no legal one-space move between them. The same applies to g5 and H5, which also share nothing but a corner.

As the next diagram shows, a Bishop on d1 can move to either a4 or A4. From this same position, it can also move to H5, though it cannot move to h5, because there is no diagonal move from g4 to h5. While g4 and H5 share a corner without sharing any sides, g4 shares a side with h5.

Queen

A Queen may move as either a Rook or a Bishop. All the examples already given for Rook and Bishop movement also apply to the Queen.

King

A King can move one space in any lateral or diagonal direction.

As in Chess, the object is to checkmate the King, and it is illegal to move it into check. Like the King in Chess, it may castle. The rule for castling is that if an unmoved King is not in check, and the castling move does not move it through or into check, and nothing is between it and an unmoved Rook, it may castle with that Rook by moving two spaces toward it with the Rook moving to the space it passed over. The only difference from Chess in this regard is that Black's King starts on a different position. So, instead of castling to c8 or g8, Black's King can castle to b8 or f8.

Knight

A Knight may leap directly to any non-adjacent space that may be reached by the combination of a single one-space lateral move and a single one-space diagonal move. While this will give you its usual L-shaped leaps on the Chess board, it does not always work out this way on the Reroute66 board. In the diagram below, you may note that the diagram looks familiar. All the spaces the Knight on d4 can leap to are on another color, and each one appears to be two ranks and one file or two files and one rank away. However, if you examine the coordinates, you will see that its legal moves from d4 include d6, which is in the same algebraic file, and f6, which is two algebraic ranks and files away.

While a Knight normally moves to a space of a different color, it can move from A4 or H5 to a space of the same color. This is basically for the same reason that a Bishop on one of these spaces can move to spaces of a different color.

When it is vertically adjacent to the narrow end of a Switch, a Knight gets a slight boost in its mobility. This is illustrated in a movement diagram for a Knight on d3. Besides the usual spaces it can move to of a different color, it can also move to b5, which is the same color. Note that a5 and b5 are also both reachable by two lateral moves. However, this is not a reason for excluding the Knight from moving to these spaces. Each can be reached by one lateral move and one diagonal move, and neither is adjacent to a3.

When a Knight is diagonally adjacent to both spaces in a Switch, it also gets a slight boost in its mobility. This is illustrated by a movement diagram for a Knight on b3. Note that the Knight cannot go to A4, because it is adjacent to b3, but it can go to a5, which makes up for this.

From some positions, a Knight may reach either space in a Switch. This is illustrated in this diagram, which shows the legal moves for a Knight on c3 with white circles and the legal moves for a Red Knight on g7 with red circles.

Unlike the Rook, the Knight can also get an extra movement option from the branching end of a Switch. This diagram shows the legal moves for a Knight on a5 with white circles and a Knight on g4 with red circles. Besides the usual moves to spaces of a different color, each can also move to one space of the same color. For the Knight on a5, b3 is reachable by a lateral move to A4 and a diagonal move to b3. For the Knight on g4, h6 is reachable by a diagonal move to H5 and a lateral move to h6.

From some adjacent spaces on the side of a Switch, nothing appears too unusual. This diagram shows a White Knight on b4 and a Red Knight on c5. Even though these spaces are vertically adjacent, the algebraic file shifts between them. The movement pattern of each Knight looks standard, though two of the spaces that the Knight on c5 can reach are vertically adjacent.

From other positions on the board, the movement pattern of the Knight should follow the normal pattern of being able to move to any space two spaces away of a different color. Although I have provided many diagrams for the Knight, each diagram has illustrated the same rule that a Knight can leap to any non-adjacent space that can be reached by any combination of a single lateral move and a single diagonal move.

Pawn

The Pawn may move one space laterally forward without capturing. As shown below, the Pawns on a2, b4, and h6 can each move one space forward, and the Pawn on d7 cannot move to d8, because there is a piece there.

A Pawn may cature one space diagonally forward. In the diagram below, the Pawn on d7 may capture the Knight on c8, but no other Pawn has a legal diagonal move.

From a3 or h6, a Pawn may move to either space in the Switch before it, as shown for the h6 Pawn below. Also, a Pawn on b3 or g6 can capture a piece on either space of the nearby Switch. This is not shown.

On its first move, a Pawn has the option of moving two spaces laterally forward as long as its move is unblocked and it doesn't capture a piece. From a2 or h7, its double move may take it to either space in a Switch, as shown for the a2 Pawn below.

No matter which space it goes to, it may be captured by en passant if another Pawn could have captured it on the space it passed over. Since it has to pass over the same space to reach either space in a Switch, the same Pawn would be able to capture it whether or not it landed next to it. In the diagram above, the b4 Pawn would be able to capture the White Pawn by en passant if it moved to either A4 or a4.

Rules

Except where noted above, Reroute66 follows the rules of Chess. It is a straightforward adaptation of Chess to a new terrain with no additional rules.

Notes

In case you came to this game from Chess66, I will note some differences from that game here:

1. Both spaces in a Switch may be occupied simultaenously.
2. A piece in a Switch will block movement through the Switch only for paths of movement going through that space.
3. You can choose which space to land on in a Switch only if you come to it via a side or corner that both spaces in the Switch share. Otherwise, the only space a piece can go to in a Switch is the one its path of movement leads to.
4. Except for the Pawn, of course, all movement options are completely symmetrical. If a piece normally has the power to move from x to y, it also normally has the power to move from y to x.

Last revised by Fergus Duniho.