By the mid-2nd century BC, Rome controlled the west Mediterranean, policing and defending it with massive armies.
The troops had more loyalty to the generals than to distant politicians, giving men like Marius, Sulla, Pompey, and Ceasar the muscle to seize political power.
Meanwhile, peasants, whose land had been destroyed during the invasion of Hannibal in 219 BC, had flooded into Rome. They were followed by slaves and freedmen from conquered lands such as Greece, swelling the population to half a million. There was plenty of work for immigrants, constructing roads, aqueducts, markets, and temples, and financing by taxes on Rome’s expanding trade.
In 202 BC, the Roman general Scipio defeated Hannibal. Rome replaced Carthage as master of the Mediterranean.
Rome owed much of her prosperity to her skilled civil engineers. When the city’s wells were no longer sufficient, aqueducts were built to bring water from surrounding hills. Some were over 80 km (50 miles) long.