The Ciphers of the Monks
The Ciphers of the Monks is a bestselling book by American author David A. King.
The book describes in detail, a numeral system that was commonly used by European monks in the Middle Ages. That number system allowed one to write numbers from 1 to 9999 with minimum of strokes. This numeral system later fell out of use.
The system uses a vertical straight line as its main symbol. This symbol is essentially an axis that divides the two-dimensional plane into four quadrants. Each of these four quadrants signifies one of the four digits. The number can then be determined by visual inspection.
The numeral system was invented in the 1300s by French Cistercian monks. It was later replaced by the Hindu–Arabic numeral system. In any case, this numeral system later inspired several short hands and secret ciphers.