The problems with Zero
Zero is such an incredibly abstract invention of the human mind that neither the Babylonions nor the Greeks or Romans had any idea of it. (The Mayas and Chinese had some notion of zero without really any rules of how to apply it properly). The first man to establish strict rules for the use of zero was Brahmagupta.
To understand the difficulty of zero consider how to define it: Zero cannot be defined as nothing since adding 'nothing' to 'one' would not change the value from one to ten.
An even stranger thing happens if we calculate with zero. Consider first 2 x 3 = 6. We can turn that around and divide 6 : 3 = 2.
Now let's use zero: 3 x 0 = 0. If we turn that around it reads 0 : 0 = 3.
Which means that zero divided by zero equals any number from zero to infinity - not
very useful in a science that demands an exact result !