The number system used by the Romans in Antiquity used the letters of the Latin alphabet, which had different values depending on their position in the number. The digits in this system and their respective values are given in the table below:
In decimal notation, a number is formed by digits that have different values depending on the position they occupy in the number. For example, the numbers 78 and 87 use the same digits that have different values because they fill different positions in each number.
It’s important to distinguish between digits and numbers. Numbers are written with digits, but digits are not numbers: this means we cannot add or multiply them!
Interesting analogy: As a comparison, digits have the same role in numbers as letters have in words. In writing, numbers are represented by a juxtaposition of digits, just like words are represented by a juxtaposition of letters. So, 42 is a number that, with base 10, is written with the digits 4 and 2. However, just like a word can be made up of a single letter, like the word “a” (indefinite article), a single digit can represent a number. For example, base 10, the number 4 is written with only the digit 4.