On November 25, 1833, a colossal magnitude 8.7–9.2 earthquake struck off the coast of southern Sumatra, Indonesia, along the Sunda Megathrust fault. The quake unleashed enormous tsunamis that devastated coastal settlements, with waves reaching over 10 meters high and traveling as far as Sri Lanka and western Australia. Thousands perished, but with limited communication and record-keeping under Dutch colonial rule, much of the tragedy went unnoticed by the world. Nearly two centuries later, scientists uncovered the geological evidence—coral uplift patterns and sediment deposits—that revealed the true scale of the 1833 event. It was, in fact, strikingly similar to the 2004 Sumatra–Andaman earthquake, which triggered one of the deadliest tsunamis in recorded history. Both disasters originated along the same fault system, causing massive seafloor displacement and ocean-wide tsunamis. But while 1833 unfolded in silence, 2004 occurred in a connected world—one that could witness its horror but still lacked an effective tsunami warning system. The 1833 quake stands as a grim reminder that nature’s cycles are long, not forgotten. It taught scientists about the recurring megathrust events of the Indian Ocean and the importance of remembering the lessons buried in history. Because when the Earth moves again—as it surely will—the past may be the only warning we have.