Roman numeral Letter used by the ancient Romans and succeeding civilizations in Europe to represent numbers before the adoption of Arabic numerals. There were seven individual letters: I (1), V (5), X (10), L (50), C (100), D (500) and M (1000). Combinations were used to represent the numbers. From one to ten they ran: I, II, III, IV, V, VI, VII, VIII, IX and X. The tens ran: X, XX, XXX, XL, L and so on up to XC, which represented 90. The ancients used Roman numerals for commerce and mathematics. Modern applications include numbering the preliminary pages of a book and numbering paragraphs or subparagraphs in a document.

Ro·man num·er·al • n. any of the letters representing numbers in the Roman numerical system: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1,000. In this system, a letter placed after another of greater value adds (thus XVI or xvi is 16), whereas a letter placed before another of greater value subtracts (thus XC or xc is 90).