How did the Romans manage to effectively combine their whole empire into one unit?

The Romans effectively combined their whole empire into one unit through their roads. They connected people from all parts of the empire. The roads also helped the roman empire by allowing the spread of ideas and products throughout Rome, so people weren't isolated. The army also helped unite Rome. Julius Ceasar allowed people from all over become Roman citizens if they served in the army. This allowed for Rome to have a large population, and a sense of security and national pride.