Roads are built by Settlers only. Press the Road key (R key) or select Build Road from the Orders menu. Roads may not be built over Rivers until you have acquired Bridge Building. Units moving from one road square to another road square use 1/3 of a movement point regardless of terrain. Roads increase the trade generated by Grasslands, Plains, and Deserts.
Roads of good quality improved communications between cities. This was important for trade and for military purposes. Good quality roads were passable in nearly all weather, and could be traversed by wheeled vehicles much faster than bare dirt trails. This meant that mounted messengers, commercial wagons, and military units all could move from one part of the road network to another at good speed. This made it easier for centrally located armies to reach threatened frontiers. The most famous roads of antiquity were the Persian Royal Road and the Roman roads built throughout southern Europe.