
The Romans used letters to represent numbers:
The number 4 is written as IV, which meant one less than five, and 6 is written as VI, meaning one more than five.
90 is written as XC, meaning 10 less than 100. 

Roman numerals are still used today, for example on clocks, and on television or in films to show the date, e.g. 2006 is MMVI. 
Quiz 

What numbers do the following represent?
VII XVI LXXII Answer: VII is 7 XVI is 16 LXXII is 72 
How would Romans write the following numbers?
6 19 44 122 Answer: 6 is VI 19 is IXX 44 is XLIV 122 is CXXII 