X Tables
Maths History

Roman numerals and the missing zero

Use clocks, chapter numbers and treasure codes to show Roman numerals and why place value changed everything.

Quick answer

Roman numerals are an ancient way of writing numbers using letters like I, V, X, L, C, D, and M. The Romans didn’t have a symbol for zero, which made maths harder for them. When the place value system was invented, it made counting and calculations much easier.

Learning outcome

By the end of this page, you will understand how Roman numerals work and why the zero was such an important invention in maths. Success signs:
  • You can read and write Roman numerals from 1 to 100
  • You can explain why the Romans had trouble with big numbers
  • You can show how zero helps us understand place value
  • You can solve simple problems using Roman numerals

Why this matters

Roman numerals are still used today in clocks, chapter numbers, and even movie credits. But they were very difficult to use for big numbers or complex maths. The idea of zero changed everything – it allowed us to write numbers like 100, 1000, and so much more. Learning about Roman numerals and zero helps you see how maths has grown and how important it is to keep improving and inventing new ways to count and calculate.

How it works

Roman numerals use letters to show numbers:
  • I = 1
  • V = 5
  • X = 10
  • L = 50
  • C = 100
  • D = 500
  • M = 1000
We write them in order from largest to smallest. Sometimes, a smaller number before a bigger one means we subtract. For example:
  • IV = 4 (because I before V means 5 – 1 = 4)
  • IX = 9 (because I before X means 10 – 1 = 9)
The Romans did not have a zero, which made it hard to write numbers like 20, 30, 100, or 1000. They had to keep adding letters and making long, confusing numbers.

Examples you can see

Let’s look at some examples of Roman numerals:
Number Roman Numeral
1 I
2 II
3 III
4 IV
5 V
6 VI
7 VII
8 VIII
9 IX
10 X
11 XI
12 XII
20 XX
40 XL
50 L
90 XC
100 C
Let’s try to write 27 in Roman numerals:
  • 20 = XX
  • 7 = VII
  • So 27 = XXVII
Now, let’s imagine you are a Roman soldier and you need to write the number of enemies you’ve defeated. You might write:
  • 15 = XV
  • 42 = XLII
  • 99 = XCIX

Try it as a mini adventure

Adventure: The Treasure Map Challenge You are on a quest to find a treasure! You have a map with Roman numerals that tell you how many steps to walk. But there’s a problem – the map is missing some numbers and the zero is missing too! Here’s your treasure map:
  1. Walk 5 steps forward (V)
  2. Turn left and walk 10 steps (X)
  3. Walk 3 more steps (III)
  4. Find a chest with 15 coins (XV)
  5. Walk 10 more steps (X)
  6. Walk 7 steps (VII)
  7. Walk 12 steps (XII)
  8. Walk 19 steps (XIX)
  9. Find the treasure chest at 25 steps (XXV)
But wait – there’s a problem! The map says “walk 0 steps” before you start. That doesn’t make sense in Roman numerals. You need to find a way to tell your friend how many steps to take, even if it’s zero. Challenge: What number would you write in Roman numerals if you had to walk 0 steps? What would happen if you tried to write 100 or 1000 in Roman numerals?

Common mistakes

  • Mistake: Writing IIII for 4 instead of IV
    Why it happens: Some people think it’s easier to just add letters. But IV is the correct way to show 4 because it means 5 minus 1.
    Fix: Remember that when a smaller number comes before a bigger one, it means subtract.
  • Mistake: Using too many letters for small numbers
    Why it happens: Some children think they need to use more letters to make a number look bigger.
    Fix: Keep it simple – 3 is III, not IIII or IIIII.
  • Mistake: Forgetting that Romans had no zero
    Why it happens: It’s hard to imagine not having a zero in maths!
    Fix: The zero was invented later by the Babylonians and Indians, and it helps us write numbers like 10, 100, 1000 easily.

Parent and carer guide

This page helps children understand how ancient people counted and why we have a better system now. Here’s how you can help:
  • Play a game: Write some Roman numerals on cards and ask your child to read them aloud.
  • Use a clock: Point out the Roman numerals on a clock face and ask what each number means.
  • Make a chart: Create a chart with numbers 1 to 20 in both Roman and regular numbers.
  • Encourage curiosity: Ask your child why they think the Romans didn’t use zero and what it would be like without it.
  • Be patient: It might take time to get used to Roman numerals, but it’s a fun way to learn history and maths.

Practice questions

  1. What is 6 in Roman numerals?
  2. What is 18 in Roman numerals?
  3. What is 40 in Roman numerals?
  4. What is 99 in Roman numerals?
  5. What number does XXVII represent?
  6. What number does XLIV represent?
  7. Why couldn’t the Romans write 100 easily?
  8. What is the difference between writing 5 and 4 in Roman numerals?
  9. How would you write 0 in Roman numerals?
  10. What number is written as CD in Roman numerals?
Answers:
  1. VI
  2. XVIII
  3. XL
  4. XCIX
  5. 27
  6. 44
  7. Because they didn’t have a symbol for zero, so it was hard to show 100 as a clear number
  8. 4 is IV, 5 is V – it’s about subtracting when a smaller number comes before a bigger one
  9. They couldn’t – there was no symbol for zero
  10. 400

FAQ

Why did the Romans not use zero?
The Romans didn’t have a symbol for zero. They used a system of letters, and it was hard to show "nothing" or "no value" in that way. Zero was invented much later by Indian and Arabic mathematicians.

How are Roman numerals used today?
We still use Roman numerals in clocks, movie credits, chapter numbers in books, and sometimes in royal names like Queen Elizabeth II or Pope Benedict XVI.

Can you count to 100 in Roman numerals?
Yes! You can count to 100 by combining the letters I, V, X, L, and C. For example, 50 is L, 90 is XC, and 100 is C.

Why is zero so important?
Zero helps us understand place value. It shows the difference between 10 and 1, or 100 and 1. Without zero, we would have a much harder time counting and doing maths.

What comes after 1000 in Roman numerals?
After 1000, we use M. For 2000, we write MM. For 3000, we write MMM. But for very big numbers, Romans used a line above the letters to multiply by 1000.