Numbers began to emerge together with writing around 5000 BCE as humans developed agriculture and started to live together in larger groups. They needed to know the size of fields, the volume of baskets, the numbers of objects exchanged, and the taxes to be paid, and divisions of land and inheritance. To make these calculations, they used "counting numbers," or what we call “natural numbers” such as 1, 2, and 3, as well as fractions.

When people started thinking about numbers, not just using them, trouble started. Take for example the Pythagoreans, a group of students of mathematics led by the famous mathematician Pythagoras, for whom the Pythagorean theorem is named. For Pythagoras and his followers “all is number.” He is known for discovering that the relations between the notes of the musical scale can be described by ratios; he thought that ratios and proportions describe the beauty of mathematics, music, and the universe.  Irrational numbers were dangerous because they challenged the Pythagorean understanding of the world.

When Arabic numerals were introduced in Europe, they were received with suspicion, and not just because they were seen as easier to falsify in accounting. The number zero that accompanied the new numerical system presented serious conceptual
difficulties. Even mathematicians had trouble accepting it and the negative numbers it foreshadowed for a long time.

Finally, some numbers are banned even nowadays – some for historical or political reasons, while others are illegal because of the information they carry.

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