Why did the Romans build so many roads?

Over 2,000 years ago, Rome was the center of a large empire.  The Romans needed a way to move their large armies quickly so they could protect their huge country. They needed trade routes. So they joined all the parts of their empire by a network of roads.
    Beginning in 300 BC, the Romans built roads in Europe, Asia, and North Africa. By AD 200, they had built 50,000 miles of almost straight highways.
    To build their roads, the Romans sometimes had to dig tunnels through mountains. They did mot have explosives to cut through the rock. They heated the rock with fire and then threw cold water over it. When the rock cracked, they dug it out with hand tools.
    Roman soldiers and slaves built the roads without powerful machinery. They had only simple tools. Yet the roads were so well built that they were used for hundreds of years.