The Rust Sea (Sea of Rust)

The Rust Sea, also called the Sea of Rust, is Cybertron's great dead zone: an expanse of unstable planetary matter and molecular flux running along the equator, stretching between Tyrest, Polyhex, the Tagan Heights and Altihex. It is not liquid. It is a slow chemical decay of the planet's own substance, continuously venting corrosive gases that are described as unpleasant rather than immediately lethal, which is exactly the sort of hedged detail that lets writers strand characters there without killing them.

Strategically it functions as Cybertron's no man's land. Sitting between the Decepticon-held province of Polyhex and the wider planet, it is the terrain armies have to cross, and the terrain that stops them. The Hydrax Plateau rises out of its centre, and Cybertron's primary spaceport sits on the plateau, which makes the sea both the most hostile and the most trafficked region on the planet: everyone arriving from off-world lands in the middle of it.

The Rust Sea's origin is one of the more contested points in Cybertronian geography. One widely repeated account has it forming when the Crystal City collapsed beneath the surface, leaving a scar of oxidising debris where a city used to be. That account belongs to later continuities rather than to G1 proper, and it conflicts with the G1 cartoon's version of Crystal City, which the Constructicons flatten above ground in The Secret of Omega Supreme. The safest G1 reading is that the Rust Sea is simply Cybertron's oldest, most degraded terrain, a planet-sized reminder that a machine world can corrode.

• The Rust Sea and the Sea of Rust are the same place under two names; the second spelling became dominant through the War for Cybertron games.
• Cosmic rust, the metal-eating plague of the cartoon episode Cosmic Rust, is a distinct concept and is not connected to the Rust Sea.
• The Hydrax Plateau spaceport means every visitor to Cybertron arrives in the middle of its most corrosive terrain, a detail writers have used repeatedly for ambushes.
• C. Robert Cargill's unrelated 2017 science fiction novel Sea of Rust has muddied searches for this location considerably.