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.