Bardos was originally filled with ruins holding the ancient technology of the Mycenae Empire such as the Talos giants. After Dr. Hell took over he modified some of the interior parts of the island adding a command center, a hangar for the Mechanical Beasts and Gool, and even thrusters that allow Bardos to fly.
Dr. Hell discovered the island on his career of archaeology, discovering the giant robots in the ruins. But to activate them, he requested the help of roboticists including his old rival Juzo Kabuto. By the time the Talos were completed, Dr. Hell had the scientists killed with only Juzo surviving. From there he modified the island into his personal fortress. Ever since, Dr. Hell oversaw his onslaught in his quest for world domination that was obstructed by the Mazinger Z which lead an assault against the island but was rocketed into the atmosphere at the last second. However, Dr. Hell was killed by his ally Archduke Gorgon and Bardos became a base for the risen Mycenae Empire until its destruction by the Great Mazinger.