Concept of Roman Numerals
Roman numerals are a system of numerical notation used in ancient Rome and still used today in various contexts. They consist of a combination of letters from the Latin alphabet to represent numbers. Here is a detailed explanation of the concept of Roman numerals:

Basic Symbols
- The basic symbols used in Roman numerals are I, V, X, L, C, D, and M, which represent 1, 5, 10, 50, 100, 500, and 1000 respectively.

Rules for Writing Roman Numerals
- When a smaller number is placed before a larger number, it is subtracted from the larger number. For example, IV represents 4 (5-1) and IX represents 9 (10-1).
- When a smaller number is placed after a larger number, it is added to the larger number. For example, VI represents 6 (5+1) and XI represents 11 (10+1).
- The same symbol cannot be repeated more than three times in a row. To represent larger numbers, a bar is placed on top of the numeral to multiply its value by 1000.

Examples of Roman Numerals
- I - 1
- IV - 4
- IX - 9
- XL - 40
- XC - 90
- CD - 400
- CM - 900

Usage of Roman Numerals
- Roman numerals are commonly used in the names of monarchs and popes, on clock faces, for book chapters and movie sequels, and in outlines and lists to indicate the order of items.
In conclusion, Roman numerals are a unique and historical way of representing numbers that are still relevant and used in various contexts today.