Many children find it difficult to master Roman numerals at school as it is a very specific content that they are not familiar with in their daily lives. Also, having to memorize them makes it a monotonous and boring task. However, actually learning Roman numerals can be very simple if you teach children the basic keys to writing Roman numerals and the reasoning behind it.

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### What are Roman numerals? Its origin

Roman numerals are nothing more than the numerical system that was used in Ancient Rome, although their origin dates back to the Etruscans. This town that lived in Italian Tuscany had a numbering system through symbols, in which the Romans were inspired to create their numerical values.

In turn, it is believed that the numbering of the Etruscans came from the system of notches used by the ancient shepherds, which were nothing more than marks that they carved on the rods, bones and sticks to make their counts.

Based on the Etruscan symbols, the Romans created their alphabet and gave life to the Roman numerals that we know today. In the beginning, the Roman number system was governed by the additive property according to which each number that was added value to the previous one.

However, with the passage of time and with the aim of abbreviating the numbering, the subtractive property was introduced with which, depending on the position in which a number was placed, it could subtract value from the total figure. For example, at the beginning the number 9 was written as VIIII and with the introduction of subtraction it began to be written IX.

### Why is it important to learn Roman numerals?

Over the centuries the decimal numbers, inherited from the ancient Arabs who, in turn, took over from India, gained ground over the Roman numerals. That is why it is currently the system that prevails throughout the world and, therefore, the one that is taught in the educational system. However, Roman numerals are still used in some contexts, so it is important for children to master it. For example, they are used to:

- Number personalities in the line of succession as in the case of sovereigns and Popes: Philip II or John Paul II.
- Number the centuries: 19th century or 20th century.
- Number of usual dates such as anniversaries or event sessions: XXI Annual Chess Tournament or XXV Anniversary of the death of…

### Main differences between Roman numerals and decimal numbers

To learn Roman numerals it is important to understand their differences from the decimal system. One of the main differences is that the Roman numerals are made up of letters (M, C, L) while the decimal system is made up of numbers (1, 8, 9). Another big difference lies in the existence of zero. Basically, in the Roman numeration system there is no zero since it does not have any value by itself, it is not included within the Roman numerals. On the other hand, in the decimal numbering, zero is included as one more number.

This is due to, and is another significant difference between the two systems, the positional value of the numbers. Being an essentially additive system, the values of each Roman numeral are intrinsic and regardless of their position, that is, the X represents 10 in any location.

However, in the decimal system the value of a number varies according to its position. For example, the number 1 is equal to 1 unit when it occupies that position, but in the case of the number 150 it represents 100 units because it has changed its position to hundreds.

### How are Roman numerals formed? Keys to understanding how they are written and read

Basically, Roman numerals are made up of letters that, in turn, have a numerical value. The “primary” numbers are very easy to memorize since they are only seven basic letters:

- I: 1
- V: 5
- X: 10
- L: 50
- C: 100
- D: 500
- M: 1000

From the combination of these letters any Roman numeral can be formed. To do this, the letters are placed from left to right, always from highest to lowest value, except when you want to subtract a value that is placed to the right of the highest number.

For example, the number one thousand five hundred two is written MDII (M of a thousand, D of five hundred and I of one), that is, 1000 + 500 + 1+ 1. But if you want to form the number ninety-five, you write XCV (X of 10, C of 100 and V of 5) which would be 10 – 100 + 5 = 95. One peculiarity is that, starting with the number 4000, a horizontal line is used above the number to indicate that it is multiplied by a thousand.

How do you know when to add or subtract Roman numerals when forming them? Very easy. First, it should be noted that the numbers I, C and M, that is, one and its multiples, can be repeated up to three times in a row to add value while the numbers V, L and D, that is, five and their multiples cannot be written in a row since in that case, they are replaced by a greater number, that is, instead of writing VV to represent ten, X is written.

Bearing this in mind, we then resort to adding values until completing the three repetitions in the case of the number 1 and its multiples, such as, for example, to write three: III. Instead, subtraction is used when the number exceeds the allowed repetitions, as in the case of the number nine, which instead of being formed with the addition of V and four times I (VIIII), is written IX, that is, subtracting I to X.

### Main rules of Roman numerals to keep in mind

Learning to write or read Roman numerals is actually quite simple when the “primary” numbers are mastered and the basic rule for their formation is known. However, there are some rules that are important to keep in mind.

- Roman numerals are always written and read from left to right, that is, starting with the numbers with the highest value.
- Numbers followed by another of equal or lesser value are always added, such as XXII which would be 10 + 10 + 1 + 1 = 22.
- Numbers followed by a higher value are always subtracted, such as XIX which would be 10 + (1 – 10) = 19.
- The number I and its multiples X and C can be placed in front of a larger number to subtract value, but without repeating. Also, they can only subtract values from immediately higher numbers, but not from much higher values. That is, I can only subtract from V and X, C from L and C, and C from D and M.
- The number V and its multiples V and D cannot be used for subtraction in any case. For example, the number forty-five is written XLV and not VL.