The killing of eighty-two Nakan civilians by soldiers on the planet Tarakis some three centuries before Voyager passed by, commemorated by a memorial that forces visitors to relive it.
In the Voyager episode Memorial, Chakotay, Paris, Kim and Neelix return from a shuttle survey troubled by nightmares and flashbacks of a military operation. Each remembers serving under a Commander Saavdra, sent to move Nakan colonists who refused to leave. When shots were fired in the confusion the soldiers killed all eighty-two, then vaporised the bodies to hide what they had done.
Soon most of the crew share the memories. Janeway traces them to Tarakis, where an obelisk houses a synaptic transmitter that broadcasts the experience to anyone in range. Its inscription asks that the dead never be forgotten.
The transmitter is failing, and some of the crew want it shut down. Janeway decides instead to repair its power supply, leaving a warning buoy in orbit so that later travellers know what awaits them.