The game of chess attained its first surviving form sometime in the 6th Century C.E.1 There is some debate in academia whether it was India's chaturanga or China's xiangqi which developed first (most believe it was India). What there is no debate about is that the modern version of the game we recognize today certainly evolved from the Indian variant, making its way to Europe after a period of refinement in Persia. Compared to modern rules, only the Rook and Knight have remained unchanged over approximately 1,500 years. All the other pieces have had one, or multiple, changes - in some instances in direct response to an earlier rule change. Europe inherited a game fashioned after the Indian army (with a Vizier advising a King instead of an all-powerful Queen ruling beside one), updated the shape of the pieces to be more instantly recognizable to Western nobility, and between 1100 and 1500 C.E. executed one of the first tuning passes in gaming history. The rule changes began in order to speed up the opening, and bring the opponents into direct tension more quickly. The rule changes ended with the certification of the most powerful variant of a piece the game had ever known, as well as a game-breaking defensive maneuver to become known as castling.

~1000 C.E. - Extant Rules Governing Movement1
Pawn - moves 1 square straight forward. Captures 1 square diagonally forward. Promotes at 8th rank.
Knight - moves in L shape to nearest square not sharing a rank, file, nor diagonal with origin square.
Bishop - moves 2 squares along any diagonal. Jumps over friendly/enemy pieces to arrive at destination square.
Rook - moves any number of squares along rank or file until meeting a friendly piece, meeting an enemy piece, or capturing an enemy piece
Queen - moves 1 square along any diagonal (weaker than the Bishop!)
King - moves 1 square along any diagonal. No defensive maneuvers.
~1200-1300 - Special Rules for 1st Movements2
Queen - "Queen's Leap" allowed a queen, on her first move only, to jump two squares horizontally, diagonally, or straight ahead. For white's queen on D1, legal squares were B1, B3, D3, F3, and F1.
King - King's Leap allowed a king, on his first move only, to either jump like a Knight or jump two squares along rank, file, or diagonal.
~1200-1475 - Special Rules for Pawns2, 3, & 4
Pawn - "double step" allowed a pawn to move two squares forward on its first move only. Ability expired upon first capture by any piece in the game.
Pawn - en passant. "By the way, I could have captured you a year ago, so I'll capture you today even with your new rule."5
(?)1300-1475 - Expansion of Queen's role6
Queen - moves 2 squares along any diagonal, rank, or file
~1475-1492 - "The Valencian Reform"7 & 8
Bishop - moves any number of squares along either diagonal until meeting a friendly piece, meeting an enemy piece, or capturing an enemy piece
Queen - may make any move legal to either a Bishop or a Rook
~1500-1550 - Castling in its final form9 & 10
O-O and O-O-O almost certainly developed in response to the new powers of Bishop and Queen which rendered the King's Leap obsolete; mirroring how en passant responded to the pawn's "double step"5
1561 - Ruy Lopez publishes "Libro de la invencion liberal y arte del juego del axedrez" (Book of the liberal invention and art of the game of chess)11
All pieces have modern movement definitions - including pawn promotion, en passant, and castling.

G2, modern home for a fianchettoed bishop, was
originally a hidey-hole for a King's Leap2
    ABCDEFGH    
8               8
7 ¤      7
6           ¤ 6
5                                    5
4                                    4
3           ¤ ¤ 3
2 ¤      2
1           1
    ABCDEFGH    

More popular European variant of the
King's Leap was to deploy minor pieces,
bring rook over, then jump it2 & 9
    ABCDEFGH    
8          8
7      7
6           6
5                                    5
4                                    4
3           3
2      2
1 1
    ABCDEFGH    

In North Africa, artificial castling was executed by moving the King to the
2nd rank, then on a second turn moving the Rook to the King's
homesquare and the King to the Rook's homesquare9
    ABCDEFGH    
2                2
1                               1
    ABCDEFGH    
    Above, the King moves into the second rank.
Below, Rook and King move simultaneously
    
    ABCDEFGH    
2                2
1                               1
    ABCDEFGH    
    Below, final position    
    ABCDEFGH    
2                     2
1                               1
    ABCDEFGH    




Sources
1 - Wikipedia. "History of Chess". Accessed 11/14/2018.
2 - Chess.fr. "Mediaeval Chess". Accessed 11/14/2018.
3 - Wikipedia. "En passant". Accessed 11/14/2018.
4 - Wikipedia. "En passant - Historical context". Accessed 11/14/2018.
5 - Wikipedia. "Pawn (chess)". Accessed 11/14/2018.
6 - This *had* to have occurred, but we do not know when +-300 years. I posit it is most likely to have happened post-adoption of the Queen's Leap, but prior to groundbreaking expansion vis a vis Valencian Reform
7 - Chess.fr. "Valencia". Accessed 11/14/2018.
8 - LAPOC. "History of Chess Pieces". Accessed 11/14/2018.
9 - Wikipedia. "Castling". Accessed 11/14/2018.
10 - Chess.com. "Kasparov, The King's Gambit, and Opening Theory Before Castling". Accessed 11/14/2018.
11 - Wikipedia. 'Ruy Lopez' rules of chess'. Accessed 11/14/2018.

IronNoder 2018: 12/30