Dust Numerals

The flow of knowledge between Baghdad and Cordoba traveled by land and sea from the east to west and lasted for some 300 years. However, cut off and isolated from the motherland the West would always lag behind the East. Eventually the works of the ancient Greek scholars and the system of numbering from India would all make the migration westward. Inevitably, as one would expect, the great time and distance of travel caused changes to the Hindu’s numbers.

Although all were Arabs, one group considered themselves Western Arabs, and the other group Eastern Arabs. And so it was that each modified the Hindus numbers to their own liking.

The Western Arabs referred to their numbers as gobar numerals, an Arabic word meaning 'dust' because many of the Arabs wrote their works on sandy dusty slants. It is these dust numerals that are formally and historically considered the direct ancestors of the numerals we use today.

More here and here. Another fascinating history of numbers can also be found in Robert Kaplan's The Nothing That Is: A Natural History of Zero.