Chess

Chess originates from chaturanga (चतुरङ्ग), and later shatranj (शतरंज), which is also basis of several other (non-chess) abstract strategy board games.

Note that this tag is NOT for chess variants, only chess itself.

[WIP]Timeline:
Early Chess (~600 AD)
The king could move 1 space in any direction, same as modern chess.
The adviser (queen) could move 1 space diagonally. The adviser was most often used to protect the king and widely considered useless for any other purpose.
In Europe and Persia The elephant (bishop) could move exactly two squares diagonally and was not blocked by a piece in the first square. In India, only horizontal or vertical moves of exactly two squares, also allowed jumps of the 1st square. South and east of India, this piece could move 1 square diagonally or 1 square forward (representing the legs and trunk of an elephant)
The horse (knight) could move in an L-shape of horizontal moves (2 then 1 squares, or 1 then 2 squares) with no blocking by pieces in the in-between squares of the move, same as modern chess
The chariot (rook) could move horizontally or vertically any number of spaces but could be blocked. Same as modern chess.
The foot-soldier (pawn) could move one square forwards and capture by moving one square diagonally forward. There was no two-square option (so no en passant). It could be promoted to advisor but not to any other piece.
The game was won when all pieces except the king were eliminated or a king was captured.
A record of a game played in India indicated a prohibition of stalemates. Without moving, a stalemated king could capture any piece that had him in check (it was just removed from the board and king's turn was taken). Or, the stalemated player was simply declared the winner.

Early Chess changes (~600 to ~1450)

The first rule change after the establishment of chess as we know it, was the addition of the two-square move option for pawns and soon after, the en passant capture option.

Another change was allowing the king a one time jump of any piece to a free square on the other side. This would eventually develop into the castle move.

For a time, the queen (normally allowed to move diagonally 1 space) had the option option to jump 2 spaces, even over other pieces, in any direction as her first move. This option was also applied to a new queen (promoted pawn) at times.

For a while, there was a "short assize" starting arrangement of the board. Queens began on d3 and d6. Pawns occupied the remaining columns on the 3 and 6 rows, and players could arrange all other pieces, as they liked, behind these rows.

Also, for a while, there was variant on check whereby a check could be ignored if the player capturing a king would leave their own king in checkmate as a result (remember that the game was played fully to the capture of a king or all other pieces).

The queen advances (early 12th century)
There is a record suggesting the queen moved as a modern bishop but could not be blocked.

The queen gains directions (13th century)
There is a record suggesting the queen could move as in modern chess but could not be blocked.

The Mad Queen (~1450)
"Queen's Chess". "Mad Queen Chess". "Alla rabiosa," ("with the madwoman"). "Ésches de la dame enragée," ("chess of the enraged lady"
Around 1450, the queen's modern moves, any direction, any number of spaces, and blockable, became standard. Also, the bishop's modern moves became standard. It is often assumed that the changing moves of queen and bishop went hand-in-hand. For a time, certain regions in Russia allowed the queen to also move as a knight. It is theorized that the mad queen was the reason modern checkmate and stalemate rules are what they are.

Modern rules develop (1475 to 1500 AD)
The bishop was allowed to travel any distance of unblocked squares in one of the diagonal directions.

Not yet dated[WIP]
Various modern rules once insisted that "a king can not have two queens" and "you can not have 3 knights, 3 bishops, or 3 rooks". In other wording, a pawn can only be promoted to a piece that the player has lost. This leads to the obvious, if exceedingly rare, paradox of a pawn being promoted when no pieces have been lost. These prohibitions fell out of style.

Not yet dated[WIP]
Long established rules of modern chess once had loopholes.
The rules stated that a pawn could be promoted to "any piece" Ahh, I know what you're thinking. No, not a king. Since the beginning (around 600 AD) the rules always clearly stated there could be only 1 king per player. However, the rules did not specify what color a promotion had to be. In very rare arrangements, a player could promote a pawn to a an enemy piece that would block the king into a checkmate. The rules were updated. Promotions are now segregated by color.

Castle rule change (1972)
Long established rules of modern chess once had loopholes.
The rules stated that a king and a rook could castle if neither piece had moved (among a few other stipulations). Well, when a pawn is promoted to a rook, the new rook has not moved. Thus, there was nothing preventing a vertical castling. New castling rule added: "The king and the chosen rook must be on the same rank."

Implied:
* Abstract