The Citadel of Aleppo is considered one of the oldest and largest castles in the world. The hill which the citadel rests has been used since 3000 BC. It is said the prophet Abraham milked his sheep on the citadel hill. Most of the citadel seen today is from the Ayyubid dynasty of the late 1100's-1260.
UNESCO, Buildings - Castles
In 1986 the Citadel along with the ancient city of Aleppo became a UNESCO World Heritage Site.
**As a result of the Syrian civil war the citadel has seen significant damage.
Direct link below (goo.gl)
Links: en.wikipedia.org, www.google.com