The Romans built quick straight roads because they needed to know and dominate what was happening in the far corners of their empire. Size is a function of the ability to conquer space. We talk of the world getting smaller even though its still some 24,000 miles around. The 'size' of the world is in direct proportion to our ability to span the globe, both physically and electronically. Even though the Roman Empire occupied little more than Europe, the Middle East and North Africa, in comparative terms it was probably the largest empire that ever existed, because the world was a very large place in those days.
Communications is an instrument of government.
The Romans used the roads to rule. The inheritors of their empire use the electronic media. Imperial domination, however, can take the form of more than brute force and tax collection. Most of the wars in history have been either about trade or religion. And religious wars are about the imposition of a certain weltanshung - a cosmology.