Roman numerals represent an international numbering system based on seven letters of the ancient Roman alphabet, which symbolize different numbers. The various Roman numerals are written by combining or joining letters to establish their value.

Today Roman numerals are used and are used to write dates, the numbers of certain classic clocks, to indicate the chapters of a book, or in important events worldwide, such as: to refer to the edition of the Olympics , beauty pageants or institutional anniversaries.

What is the usefulness of Roman numerals?

The Arabic numeral system is the one we use today, but although Roman numerals are not used frequently, their main uses are:

  • Name the centuries.
  • Identify the acts and scenes of the plays.
  • Name the edition of the Olympic games.
  • Number events (congresses, beauty contests, festivals, etc.)
  • Appoint the nobility and members of the dynasties (kings, emperors, dukes and popes).
  • Inscriptions and old clocks.
  • Number the chapters or volumes of a book. (Book I, Volume IV, Chapter XI).
  • Write the years on tombstones.
  • Identify the year of a film or television production.

History of Roman numerals.

The Romans had a great empire that encompassed much of Europe and spread across the north of the African continent. The peoples subdued by the Romans learned a lot from them in terms of their culture, their language (Latin), their customs, their writing and especially the type of numbering used by the Romans.

When the Roman Empire disappeared, the things that were learned from them remained, but they changed as the centuries passed. Among them we find the language, because today we speak Spanish, which comes from Latin.

But the Roman numerals with the passage of time were disappearing and were replaced by the Arabic system, from India, which the Arabs extended and is the one we use today since it is much easier to use.

Roman numeral rules

Roman numerals are governed by the following rules:

  1. Roman numerals are represented by seven capital letters which are:

 I=1, V=5, X=10, L=50, C=100, D=500 y M=1000.

  1. They are written and read from left to right.
  2. The letters I, X, C, M can be repeated a maximum of 3 times within the same number (III = 3, CCC = 300 and MMM = 3000)
  3. The symbols V, L, D can appear only once (IIIV = 8, CLV = 155, CD = 600).
  4. If a smaller symbol is followed by a larger one, the value of the first subtracts from the second (IV = 4).
  5. If a larger symbol is followed by a smaller one, the two values ​​are added (XII = 12).
  6. In particular, if a symbol is enclosed in two of higher value, it must be subtracted from the one to its right. The number 400 is written CD (subtracting 100 from 500).
  7. Only the symbols I, X, C can be used for subtractions and can only be subtracted once.
  8. The symbol that is subtracted can never be less than one-tenth of the value from which it is subtracted.

To refer to numbers greater than 1,000, the Romans respected these rules about the composition of Roman numerals, using the following methods:

  • To multiply a number by 1,000 : write a line over a symbol.
  • To multiply a number by 100,000 : border the symbol with two vertical lines on the sides and a horizontal line above it.
  • To multiply a number by 1,000,000 : two horizontal lines are placed over a Roman symbol.

Other rules for subtracting Roman numerals are:

  • The symbol can only subtract from the V and X symbols.
  • The symbol X can only subtract from the symbols L and C.
  • The symbol C can only subtract from the symbols D and M.

Example of Roman numerals

Let’s look at some examples to understand the above rules:

  • The number 15 written as a Roman numeral would be XV instead of VVV. In this case rule 4 applies according to which the symbol V can appear only once. Rule 6 is also used, where the largest number is added to the smallest by being in front of it.
  • To write the number 400 , the correct form would be CD . If we were to write CCCC it would be an error, because according to rule 3 the symbol C = 100 can only appear three times. In this case, rule 7 applies, which indicates that if there are two symbols of great value, the one on the right subtracts the other.
  • The number 99 is represented as XCIX and not IC since I = 1 is one hundredth of C = 100 and therefore it would break rule 8.
  • Another example, the number 1,999 is written in Roman numerals as MCMXCIX , instead of MIM. This number is organized as follows: M (1,000), CM (900), XC (90), IX (9) = MCMXCIX (1,999).

How to write Roman numerals with ease?

If you want to learn to write Roman numerals easily, you just have to follow the following guidelines:

  1. Understand the basic Roman symbols , which are as follows:

I = 1

V = 5

X = 10

L = 50

C = 100

D = 500

M = 1.000

  1. Learn all the digits from 1 to 9 , which are:

I = 1

II = 2

III = 3

IV = 4

V = 5

VI = 6

VII = 7

VIII = 8

IX = 9

  1. Learn all the tens from 10 to 90 , which are as follows:

X = 10

XX = 20

XXX = 30

XL = 40

L = 50

LX = 60

LXX = 70

80 = 80

XC = 90

  1. Learn all the hundreds from 100 to 900 , which are:

C = 100

CC = 200

CCC = 300

CD = 400

D = 500

DC = 600

DCC = 700

DCCC = 800

CM = 900

  1. Learn to write numbers greater than 1,000. Since the M represents the number 1,000,

and if you want to write 1,000,000, you just have to add a line over the symbol to represent it. The line above the tall symbols represents a thousand times that amount. So it’s like multiplying 1,000 x 1,000 or in Roman numerals it would be M x M = 1,000,000.

To represent 5,000,000, you will have to write MMMMM putting a bar above it

To each M. This is done this way because the M is the symbol with the highest value in Roman numerals.

  1. How to write compound numbers. To write composite numbers in Roman numerals, the rules governing these numbers must be followed. For instance:

Writing the number 2,968 is written as MMCMLXVIII because:

The first letter M = 1,000.

The second letter M = 1,000.

The following letters CM = 900. (C = 100 minus M = 1000 equals 900).

The following letters LX = 60. (L = 50 plus X = 10 equals 60).

The following letters VIII = 8. (V = 5 plus III = 3 equals 8).

Therefore, you will get 2,968 if you put all the symbols together.

Operations with Roman numerals

Roman numerals can be considered fancy scripts, but they are essentially unusable for calculations. The actual calculation was made by the Romans with the abacus. But if you want to know how to add with Roman numerals, you have to follow the following steps:

  1. Convert the subtractions into additions.
  2. Join the two numbers you want to add.
  3. Sort the symbols in descending order according to their value.
  4. Sum internally from right to left.
  5. Convert back to subtraction respecting the rules of Roman numerals.

Let’s see the following example: Add 145 + 79 = 224

  1. Write each amount in Roman numerals: CXLV + LXXIX
  2. Pasa 145 a 135 y 79 a 78
  3. Join the two numbers: CXXXXVLXXVIIII
  4. Order them CLXXXXXXVVIIII
  5. Add VV = X. CLXXXXXXXIIII remains. Go XXXXXXX to LXX. Then there is CLLXXIIII. And LL = C, leaving CCXXIIII
  6. Go to subtractions in the corresponding places: IIII = IV. And voila, we have the correct result: CCXXIV = 224
Now if you want to subtract two quantities in Roman numerals, the steps are simpler than in addition. And these are:
  1. Convert the subtractions into additions.
  2. Eliminate the common symbols of the two quantities.
  3. Expand the largest number in the subtrahend and take the first symbol of the minuend and expand it. Then reapply step 2.
  4. Go back to subtraction in the necessary places.

Let’s see the example of this subtraction: 241 – 85 = 156

  1. Write the amounts in Roman numerals: CCXLI – LXXXV
  2. Pass CCXLI to CCXXXXI and LXXXV leave it the same.
  3. Take XXX out of the two quantities. Remaining CCXI and LV
  4. Since L is the largest number in the subtrahend, expand a C in the minuend leaving CLXXXXXXI and LV . Now remove the L from the two numbers and there are CXXXXXXI and V.
  5. Now since V is the only symbol that remains of the second number, expand an X of the first as V = IIIII, leaving CXXXXXVIIIIII and V. Remove the V from the two and it remains CXXXXXIIIIII .
  6. Following the rules of Roman numerals, the final result is CLVI = 156

Curiosities of Roman numerals

  • The ancient Romans did not have a symbol to indicate zero, they did not possess the concept, because numbers were used to count what we had.
  • There are no Roman numerals to represent relative numbers, decimal numbers, and fractions.
  • Due to its structure, the Romans could not use their numbers to perform arithmetic operations: to add or subtract they used the abacus.

Conclusion on the use of Roman numerals

In conclusion, the Roman numeral system was of great impact due to the influence of the Romans in the history of the world. Thanks to this, Roman numerals have endured to this day and although it is not a perfect numbering system, it is currently used in specific areas, fulfilling its function well.

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Dr. Samantha Robson ( CRN: 0510146-5) is a nutritionist and website content reviewer related to her area of ​​expertise. With a postgraduate degree in Nutrition from The University of Arizona, she is a specialist in Sports Nutrition from Oxford University and is also a member of the International Society of Sports Nutrition.

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