A merchant wants to sail from the Mediterranean into the Black Sea. Which fact about the Byzantine capital explains why its rulers could control that voyage?
It lay far inland among the great rivers of central Europe, well away from any coast.
It stood on the narrow strait joining the two seas, at the crossing between Europe and Asia.✓Correct answer
It was built on the Rhine frontier, where the old Roman defences guarded the river crossings.
It stood beside the Danube, and the river carried its trade down towards the sea.
Explanation
Ships passing between the two seas had to use one narrow channel, so a city set on that channel could watch, tax or close everything that went through, and that is where its rulers drew their advantage. The river-frontier answers fail because a position on the Rhine or the Danube controls movement along or across a river, not the sea passage this merchant has to use.