In Greek and Roman mythology, the 3-headed dog Cerberus guards the gates of Hades. Cerberus permitted souls to enter the realm of dead, but allowed none of them to leave. Only a few ever managed to sneak past the creature, among them Orpheus, who lulled Cerberus to sleep by playing his lyre, and Hercules, who brought Cerberus to the land of the living as the last of his 12 labors.
A different type of Cerberus guards the gates of US military Forward Operating Bases. Cerberus is a portable integrated tower with mounted sensors, developed to provide persistent ground surveillance for FOB perimeter defense. Alone, a Cerberus unit can provide surveillance for a specific region at a given time. Networked, multiple Cerberus towers form a mesh network, communicating autonomously with each other to act as a virtual fence.