What did Hadrian do to change today?

Hadrian stopped expanding the Roman Empire, building walls around the boundary. He probably stopped the empire crumbling quicker and therefore saved the spread of Christianity. Alternative Contrary to Augustus' dictum of securing the borders by defensive frontiers (mostly rivers - Rhine-Danube, not walls) and diplomacy, Hadrian expanded the empire - completing the subjugation of Dacia and capturing Mesopotamia. These extra frontiers created extra areas of potential conflict, and were virtually indefensible. However his time was not one of great external threat - this began a century later. So the help to the expansion of Christianity did not have any real impact - in fact the barbarians who eventually overran Rome had mostly converted to Christanity. His influence on today's world is negligible.