Qam-Chee was a city on the Klingonhomeworld of Qo'noS. It was there in approximately 1373 that Kahless and the Lady Lukara fought a pitched battle in the city's Great Hall against the soldiers of Molor. While the rest of the city's garrison fled before Molor's five hundred soldiers, Kahless and Lukara stood their ground and defeated the forces. Shortly after their victory the two began their great romance, the stuff of Klingon legend. (DS9: "Looking for par'Mach in All the Wrong Places")
In DS9: "Looking for par'Mach in All the Wrong Places" taking place in 2373, Worf enthusiastically mentioned the events in Qam-Chee to have happened "a thousand years ago." This would appear to be somewhat of a contradiction as TNG: "Rightful Heir" and TNG: "Firstborn" both state, that Kahless lived five hundred years earlier. Either Worf "rounded" the number of years in his enthusiasm, or Molor and Kahless were at least 500 years old, which, while the maximum life span for Klingons has never been clearly defined, seems to be without precedent. Another solution would be that Worf counted in Klingon years, as 2373 corresponds to the Year of Kahless999.