As an expert in the field of Roman numerals, I can explain that they are a numeral system that originated in ancient Rome and were used throughout the Roman Empire. The system uses a combination of letters from the Latin alphabet: I, V, X, L, C, D, and M, where the value of a letter is determined by its position relative to other letters.

The Roman numeral "Mmiii" can be broken down as follows:

- M stands for 1000.
- The second M is not standard and typically would not be used in Roman numerals as the system does not use repetition of the same letter to indicate multiplication or addition.
- iii stands for 3 (1 + 1 + 1).

However, the use of two M's one after the other is not conventional and could be a mistake or a misunderstanding. If the intention was to represent a larger number, it would typically be written with a line over the top of the repeated numeral or with the numerals in a different order to indicate multiplication or addition.

In standard Roman numeral usage, "Mmiii" would be incorrect. If we were to interpret the first M and the iii separately, it would be "1000 + 3," which equals 1003. But with two M's, it's unclear and not a standard representation.

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Enter a whole number such as 2003, or a Roman numeral such as MMIII, then click Convert. The input must be in the range of 1 - 4999, or I to MMMMCMXCIX. The Basics. A smaller number in front of a larger number means subtraction, all else means addition.read more >>