What is the roman numeral for 1000000000?

Answer 1

First consider the following: (M) or M with an horizontal bar above it are both the equivalent of a million but M on its own is the equivalent of a thousand.

There are manuscripts that still exist today dating back to the Middle Ages that show that the Roman numeral system sometimes used superscript numerals to indicate multiplication similar to what we do today to denote powers of numbers with exponents.

For instance: 10000 is written out as XM meaning 10*1000 = 10000.

Likewise one billion would work out as (M)M meaning 1000000*1000 = 1000000000.