Transport in Papua New Guinea is heavily limited by the country's mountainous terrain. As a result, air travel is the single most important form of transport for human and high density/value freight. Aeroplanes made it possible to open up the country during its early colonial period. Even today the two largest cities, Port Moresby and Lae, are only directly connected by planes. Port Moresby is not linked by road to any of the other major towns, and many remote villages can only be reached by light aircraft or on foot.