Pancrase dates back to the times of ancient Greece and was actually one of the Olympic sports one could compete in. Pancrase was just as popular as Wrestling and Boxing. This sport only began to die out after the Romans took over and tried to make this sport more "interesting" by introducing gloves with spikes into this sport. These gloves removed much of the technical aspect of the game and soon died out (a lot of famous pankrationists even refused to partake in this new 'bloodsport' because of the supposed lack of skill).
As an interesting fact, probably the three most popular sports were Wrestling, Boxing, and Pancration. A competitor in one event would most likely compete in the others as well. The sport that was regarded to be most dangerous wasn't Pancration, however, but boxing. Just about all the competitors requested for their Pancration matches to be first so they could compete in the boxing event without injuries.
Yeah I wrote an english paper on MMA a year ago
.