The proto-Arabian horse may have been domesticated by the people of the Arabian peninsula known today as the Bedouin, some time after they learned to use the camel, approximately 4,000–5,000 years ago. One theory is that this development occurred in the Nejd plateau in central Arabia. Other scholars, noting that horses were common in the Fertile Crescent but rare in the Arabian peninsula prior to the rise of Islam, theorize that the breed as it is known today only developed in large numbers when the conversion of the Persians to Islam in the 7th century brought knowledge of horse breeding and horsemanship to the Bedouin. The oldest depictions in the Arabian Peninsula of horses that are clearly domesticated date no earlier than 1800-2000 BCE.