When men started writing they began to use symbols to represent units or small bundles of units. These symbols were called numerals, or numbers, and represent specific quantities. In 628, Brahmagupta formalized Zero (0), which is a symbol and a number. Roman numerals were found to be limiting and time consuming, so the Indians proposed using fewer symbols and changing their order. They created a type of grammar for mathematics, based on the number 10, that would be adopted by the entire world. Brahmagupta explained that numbers that were less than zero could also be counted, called negative numbers. All these numbers represented whole quantities, so were called whole numbers. Fractions were invented to indicate part of a whole number, with the parts of the whole being called the numerator, and its equally divided pieces the denominator. Based on the Latin word ratio, these were called rational numbers. In 1427, Al Kashi proposed writing these numbers as decimal fractions, which was later simplified by Simon Stevin and then again by John Napier to be known as a decimal.