How did our system of counting begin?

It seems very natural to you taht if you have two pennies and you add two pennies to them, you have four pennies. But did you know it may have taken man millions of years to be able to think this way? In fact, one of the most difficult things to teach children is the concept of numbers.
In ancient times, when a man wanted to tell how many animals he owned, he had no system of numbers to use. What he did was put a stone or pebble into a bag for each animal. The more animals, the more stones he had. Which may explain why our word "calculate" comes from the Latin word Calculus which means "stone"!
Later on, man used tally marks to count. He would just scratch a line or tally mark for each object he wnated to count, but he had no word to tell the number.
The next step in the development of the number system was probably the use of fingers. And again we have a word that goes back to this. The word "digit" comes from the Latin word Digitus, which means "finger"! And since we have 10 fingers, this led to the general use of "10" in systems of number.
But in ancient times tehre was no single number system used all over the world. Some number systems were based on 12, others were based on 60, others on 20, and still others on 2,5, and 8. The system invented by the Romans about 2,000 years ago was widely used by the people of Europe until about the 16th century. In fact, we still use it on clocks and to show chapters in books. But it was a very complicated system.
The number system that we use today was invented by the Hindus in India thousands of years ago and was brought to Europe about the year 900 by Arab traders. In this system all numbers are written with the nine digits 1,2,3,4,5,6,7,8,9 to show how many, and the zero. It is a decimal system, that is, it is built on the base 10.