The largest of Aleppo's khans, Khan al-Gumruk (or al-Joumruk), was built in 1574 by the Ottoman governor, Hanzade Mehmet Ibrahim Pasha, in the heart of the covered Aleppo souk. It housed banks, as well as the consulates of French, British and Dutch commerce, and thus became the centre for foreign trading and diplomacy. Gumruk translates to "customs", which perhaps accurately describes the function of Khan al-Gumruk in the 16th/17th centuries when it was frequented by foreign merchants. Khan al-Gumruk continues to house approximately 250 shops to this day, mostly specialising in textiles.
IMPORTANT UPDATE: Based on a Youtube video posted in October 2012, Khan al-Gumruk suffered some damage because of the shelling by the Syrian government forces. In the footage I saw, the dome had a hole through it.
Is massive khan, Khan It was built in 1574 by the Ottoman governor, al-Gumruk Has more than approximately 250 shops from cloth to whatever you want jewerly leather etc.is like amaze inside but shopkeepers are really friendly you will be invited for some tea or coffee while hanging around.
so do not hasitate to sit at soem shops when you can tired.