The word highway was originally used for roads constructed in the ancient Roman Empire. The Roman emperors had constructed 80,000 kilometers network of highways connecting about 200 towns and cities of the empire. All these roads were skillfully constructed and metalled for the rapid movement of cavalry and military chariots to any part of the sprawling empire. These roads were also constructed somewhat higher than the ground to afford greater range of visibility all around as a defensive strategy against ambushes and enemy attacks. Another advantage of the roads at a level higher than the ground was that they remained free from water logging. All the major Roman roads came to be known as highways because of their higher level. Subsequently any major road linking two cities in other countries also came to be known as highway.