The question "How many?" prompted early civilizations to make marks to record the answers. The words and signs used to record how many were almost surely related to our body parts: two eyes, five fingers on one hand, twenty fingers and toes. For instance, the word "digit," which we use for the symbols that make up all our numerals (0, 1, 2, 3, 4, 5, 6, 7, 8, 9), is the Latin word for finger.

This ancient Egyptian calendar with Zodiac symbols was used by Greek scholars in Alexandria for astronomical calculations.

These first numbers are now called the set of counting numbers: {1, 2, 3,…}, and sometimes this set is called the natural numbers. Notice that the counting numbers do not include 0. Whereas some early cultures, including the Egyptians, the Chinese, and the Mayans, understood the concept of zero, the digit 0 did not appear until some time after the other nine digits.

In the earliest development...