I just found this out recently, and it was SOOOOO cool, so I just had to turn it into a project idea.
Cistercian numbers are a medieval numeral system that allows any number from 1 to 9,999 to be represented as a single glyph using a central stave and quadrant-based strokes. Cistercian numerals were developed by the Cistercian monastic order in the early 13th century, around the same time Arabic numerals were introduced to northwestern Europe. The system was designed to be compact and efficient, enabling monks to write numbers from 1 to 9,999 using a single symbol. Each number is constructed around a central vertical or horizontal stave, with small lines or strokes added in four quadrants to indicate place value.
