The nr. zero was invented
independently in India and by the
Maya. In India a decimal system was
used, like ours, but they used an
empty space for zero up to 3rd Century
BC. This was confusing for an empty
space was also used to separate
numbers, and so they invented the dot
for a zero. The first evidence for the
use of the symbol that we now know as
zero stems from the 7th century AD.
The Maya invented the number zero for
their calendars in the 3rd century AD.
The number zero reached European
civilisation through the Arabs after
800 AD. The Greek and Roman did not
need the number zero for they did
their calculations on an abacus. The
name 'zero' comes from the arabic
'sifr'. (Data from the book "the
calender" by D. E. Duncan).