In Europe, Roman numerals were used until up to the Middles Ages. So to write 138, you essentially had to write 100+10+10+10+5+1+1+1, i.e. CXXXVIII. With this system, arithmatic operations were inevitably extremely complicated.

At the same time in India,a much better system was in place: each number, including zero, was represented by a symbol. So then, to express the idea of ‘one dozen’, one only had to write the symbol ’1′ followed by  the symbol ’2′.

The Arabs, being ingenious mathmaticians and mighty travelers, immediately understood the inherent value in the Indian system; they adopted it and spread it up to the Middle East. It was here, in the 10th century, that Europeans finally discovered this system and adopted it for themselves.

Since these numbers were in use by the Arabs, the Europeans called them ‘Arabian numerals’, ignorant of their true Indian origin. For what it’s worth, these ‘Arabic numbers’ are in Arabic called ‘Hindu numbers’.