The city Rome was built up through organization and planning, also with a few lucky breaks. The development of the Roman Empire followed the same exact layout. Rome was able to successfully conquer and control their empire through their strong military, government, and some choice geography.
The military of Rome could not be matched. It was organized down to every last soldier. It started with groups of some 5,000 men, wearing armor from head to toe, called a Roman legion. Each legion was then divided into smaller groups called centuries having eighty men. Then the Calvary, soldiers on horseback, gave extra support to the initial legion. This set up allowed any century of the legion to act alone, letting the army as a whole focus on many different things at one time. To top off the great strategically organization of the army, each soldier went through extensive training, producing some of the fiercest and skilled warriors of the ancient times. Moreover, the Roman military believed in the greatness of Rome and were very loyal and devout. Joining army was thought to be a worthy cause and for a lot of people a better way of life. In the army each soldier was introduced to Roman the roman lifestyle and culture. When they weren't fighting in wars the Army was put to work benefiting the empire with bridges, roads, canals, aqueducts, and even ports. The same attitude during war went into to work, allowing the Romans to complete huge projects in a short time. No other military system has ever had the same essence as the Roman Military.
Rome had a strong and steady government. It was headed by an emperor, who was an absolute ruler. Augustus was the founder of this government. He ruled with a mighty and fair hand. Having the support of the military, he managed to maintain the borders of the Empire and protect it form invasion. He paid government officials to handle grain supply, tax collection, and he even started a mail system.