The Need for Zero

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The Roman Numeral representation for 2001 is MMI without any gap.
But the decimal value needs zeros in the Hundreds and Tens columns
to make it clear that the 2 is in the Thousands column.

Example  5030

0 in the	Units column has a place value of	0 x 1 =	0
3 in the	Tens column has a place value of	3 x 10 =	30
0 in the	Hundreds column has a place value of	0 x 100 =	0
5 in the	Thousands column has a place value of	5 x 1000 =	5000

The following provides a comprehensive discussion of zero:
A history of Zero - [st-andrews.ac.uk]