The most important geographic factor to the growth of the Byzantine Empire was its control over the Bosporus Strait, which connected the Black Sea to the Mediterranean Sea. This strategic location allowed the Byzantines to control trade between Europe and Asia, and gave them a major advantage in military defense. The Bosporus Strait was also a key factor in the Byzantine Empire's ability to maintain its independence from the Arab caliphates, which controlled much of the Middle East during the early centuries of the Byzantine Empire.