I'm in memory block 4. I am supposed to go the rich district of Damascus, but I can't access it. There is a huge wall between the Rich and Poor district blocking access. Only the Poor district is open to me, as has been the case since the start of the game. So... how do I unlock the rich district?
This video demonstrates one route from the Bureau to a Viewpoint in the Rich District: http://www.thehiddenblade.com/stuck-memory-block-4-damascus --- Maps for all AC2 and AC:B collectibles: http://www.thehiddenblade.com/maps