Try to imagine a day without numbers. Try to imagine getting through the first hour of that day. No alarm clock, no time, no date, no television or radio, no stock market report or sports results in the newspapers, no bank account to check.
The fact is, our lives depend on numbers. You may not have "a head for figures", but you certainly have a head full of them. Most of what we do each day is conditioned by numbers. Indeed, the degree to which our modern society depends on those that are hidden from us was made clear by the financial meltdown in 2008, when overconfident reliance on the advanced mathematics of the credit market led to a collapse of the global financial system.
How did we become so familiar with, and so reliant on, these abstractions that our ancestors invented just a few thousand years ago? By the latter part of the first millennium AD, the system we use today to write numbers and do arithmetic had been worked out – expressing any number using just the 10 numerals 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and adding, subtracting, multiplying, and dividing them by the procedures we are all taught in primary school. This familiar way to write numbers and do arithmetic is known as the Hindu-Arabic system, a name that reflects its history.
Before the 13th century, however, the only Europeans aware of this system were, by and large, scholars, who used it solely to do mathematics. Traders recorded their data using Roman numerals, and performed calculations either by using their fingers or with a mechanical abacus.
That state of affairs started to change soon after 1202, the year a young Italian man, Leonardo of Pisa, whom a historian centuries later would dub "Fibonacci", completed the first general-purpose book of arithmetic in the West. Liber abbaci explained the "new" methods in terms understandable to ordinary people – and its influence did as much as any other book to shape the development of modern Western Europe.
Leonardo had learnt about the Hindu-Arabic number system when his father took him to the north African port of Bugia (now Bejaïa, in Algeria) in around 1185. Years later, his book would provide not only a bridge that allowed arithmetic to cross the Mediterranean, but also one between the mathematical cultures of the Arabic and European worlds. It was an act every bit as revolutionary as the one carried out by personal computer pioneers in the Eighties who took computing from a small group of "computer types" and made it available to, and usable by, anyone. Not only did the appearance of Liber abbaci prepare the stage for the development of modern algebra and hence modern mathematics, but it also marked the beginning of the modern financial system and the way of doing business that depends on sophisticated banking methods.