Fortress chess (or Russian Four-Handed chess) is a four-player chess variant played in Russia in 18th and 19th centuries. The board contains 192 squares including the fortresses at its corners. The fortresses contain 16 squares and various pieces are placed inside.
- Pritchard, D. B. (1994). "Fortress Chess". The Encyclopedia of Chess Variants. Games & Puzzles Publications. pp. 111–12. ISBN 0-9524142-0-1.
- Pritchard, D. B. (2007). "Fortress Chess". In Beasley, John. The Classified Encyclopedia of Chess Variants. John Beasley. pp. 324–25. ISBN 978-0-9555168-0-1.