1970 in Roman numerals

How MCMLXX is built

Roman numerals are written one decimal place at a time, largest first.

1. Mthousands · 1M is 1,000.
2. CMhundreds · 9C before M means 1,000 − 100 = 900. This saves writing DCCCC.
3. LXXtens · 7L (50) plus XX (20) makes 70.

1,000 + 900 + 70 = 1,970

The pair CM uses subtraction: a smaller letter before a larger one is taken away from it. Only six pairs work this way: IV, IX, XL, XC, CD and CM. More on subtraction

Mistakes to avoid

• Not MLMXX. It looks like a shortcut, but L is never written before a larger letter to subtract. The correct form is MCMLXX.
• Not MDCCCCLXX (9 letters). That adds everything up without subtraction. The Romans sometimes wrote numbers this way, and clocks still show 4 as IIII, but today MCMLXX (6 letters) is the standard.
• There's no letter for zero. The zero is simply left out, which is why 1970 has 3 parts, not 4.