Roman Numerals

Roman numerals - Numeral system derived from ancient Rome based on the principle of addition and subtraction.

Symbol	Value	Name
I	1	unus
V	5	quinque
X	10	decem
L	50	quinquaginta
C	100	centum
D	500	quingenti
M	1000	mille

Roman numerals are based on Latin letters with assigned numerical values. Romans adopted their numeral system from the Etruscans. The original system was modified in the Middle Ages, resulting in the Roman numerals used today.

Roman numerals are used, for example, for numbering chapters in books, in numerical lists, marking volumes of works, and writing dates.

Rules for Writing Roman Numerals

Arranging the symbols according to the principle of addition and subtraction yields intermediate values between the symbols, following these rules:

• Repeating a symbol means addition (e.g., II = 1 + 1 = 2, XX = 10 + 10 +10 = 30);
• A smaller numeral following a larger numeral means addition (e.g., VI = 5 + 1 = 6, CLV = 100 + 50 + 5 = 155);
• Up to three identical symbols may follow each other (e.g., not IIII but IV);
• A smaller numeral preceding a larger numeral means subtracting it (e.g., IX = 10 – 1 = 9, CM = 1000 – 100 = 900);
• Only one symbol may precede another (e.g., 80 is not written as XXC but as LXXX);
• The symbol I can stand only before V and X, X before L and C, and C before D and M (e.g., 99 is written as XCIX, not IC);
• Symbols V, L, and D are not repeated;
• The Roman numeral system does not include the concept of zero.

Roman numerals are used, for example, on clock faces, where the number 4 is often represented using the unconventional Roman numeral IIII.

For 98 and 99, Roman numerals IIC (duodecentum) and IC (undecentum) are sometimes used.