Linked from
The 19 pages that link to Roman numerals, each with the reason it gives.
Positional notationCompared with: Its symbols largely retain their values regardless of position.
Numeral systemCompared with: Its symbols do not generally encode place value, unlike decimal digits.
DigitCompared with: Roman numerals show that digits need not be positional or include zero.
BaseCompared with: Roman numerals are not a positional system with a fixed base.
Numerical digitCompared with: Its symbols do not generally work as digits in a positional system.