Communication from the front lines to the rear areas and laterally across the front informed commanders of the location and activities of friendly and enemy forces, and enabled them to move or re-position units for attack or defence. Telephone wires maintained by military signallers were the principal means of communication, but these were often cut by high explosive shells, demanding frequent and dangerous repair efforts. Other means of communication included message-carrying pigeons, flags, and human runners. Certain messages could be transmitted using Morse code and signalling lamps. These portable lamps aimed a focused beam of light at a receiving signaller. They could transmit over long distances much faster and more safely than a runner exposed to enemy fire.