A Rook is of the value of five Pawns and a fraction, and may be exchanged for a minor Piece and two Pawns. Two Rooks may be exchanged for three minor Pieces.
Howard Staunton (1873). “The Chess-player's Handbook: A Popular and Scientific Introduction to the Game of Chess, Exemplified in Games Actually Played by the Greatest Masters, and Illustrated by Numerous Diagrams of Original and Remarkable Positions”, p.34
