A camel train or caravan is a series of camels carrying passengers and/or goods on a regular or semi-regular service between points. Although they rarely travelled faster than the walking speed of a man, camels' ability to withstand harsh conditions made them ideal for communication and trade in the desert areas of North Africa and the Arabian Peninsula for centuries, though they could only travel on routes with sufficient sources of food and water. Camel trains were also used sparingly elsewhere around the globe but during the 20th century they have been largely replaced by motorized vehicles or air traffic.