No Full Synchronisation Requirement
When you arrive at the map marker, climb the tower to the top and find the mission start indicator. Stay up there and use Eagle Sense to look around in the direction of the aqueduct to the northeast. It has three symbols on or surrounding it, as in the last part of this ongoing mission. Scan the centre one and that should lead to the book. Jump there from a nearby rooftop using the hookblade for a little more reach.
Head to the nearby marker in a cemetery-like area and find the similar doorway to the one from the Polo trading post to being the next Memory.