The first rule - Roman numerals set of basic symbols
Roman numerals set of basic symbols:
A. The major numerals, the symbols that were used to build the rest of the numbers in the Roman numeral system:
I = 1 (one);
V = 5 (five);
X = 10 (ten);
L = 50 (fifty);
C = 100 (one hundred);
D = 500 (five hundred);
M = 1,000 (one thousand).
At the beginning, Romans did not use numbers larger than 3,999, having no representation for larger numbers such as: 5,000, 10,000, 50,000, 100,000, 500,000 or 1,000,000. These numbers were added later on and for them various different notations were used.
Thus, initially, the largest number that was written with Roman numerals was: MMMCMXCIX (3,999).
B. The numerals below were a later addition to the Roman numeral system; these numerals were also written with an overline or between two vertical lines, to indicate multiplication by 1,000. We prefer writing them between brackets instead because 1) it's more accessible to computer users when compared to the overline and 2) it avoids any possible confusion between vertical lines and the symbol for one - I.
V or |V| or (V) = 5,000 (five thousand);
X or |X| or (X) = 10,000 (ten thousand);
L or |L| or (L) = 50,000 (fifty thousand);
C or |C| or (C) = 100,000 (one hundred thousand);
D or |D| or (D) = 500,000 (five hundred thousand);