Aleppo is one of the oldest continuously inhabited cities in the world; it may have been inhabited since the 6th millennium BC. Excavations at Tell as-Sawda and Tell al-Ansari, just south of the old city of Aleppo, show that the area was occupied by Amorites since at least the latter part of the 3rd millennium BC.
Such a long history is attributed to its strategic location as a trading center midway between the Mediterranean Sea and Mesopotamia
For centuries, Aleppo was the largest city in the Syrian region, and the Ottoman Empire's third-largest after Constantinople and Cairo. It was also one of the largest cities in the Levant before the advent of the Syrian Civil War.
According to wikipedia