They originated in India in the 6th or 7th century and were introduced to Europe through the writings of Middle Eastern mathematicians, especially al-Khwarizmi and al-Kindi, about the 12th century. They are very different from previous methods of counting, such as the abacus, and paved the way for the development of algebra. In the past many other systems were used. Fibonacci popularized the Hindu–Arabic numeral system to the Western World.