Bread and Circuses
A planet identical to Earth is discovered, with one difference: Rome never fell. Ancient barbarism and 20th century technology combine to create a deplorable and inpenetrable society.
We'll admit we're suckers for these "cultural parallel" episodes; they're really more enjoyable than adventures aboard the ship. He's a genuinely interesting idea in the "what if?" science fiction/ history tradition, though the reasons why Rome didn't fall are probably as complex and disputed as the reasons why it did in our world. The question then becomes, what would "contemporary Rome" be like? Well, they have Jupiter 8 cars, gladiator games on TV, and slavery. This will never do! But Kirk can't interfere with the planet's development. A dilemma. But there's little time to ponder as he's captured, tortured, seduced, and forced to watch his friends battle in the arena. (There's a switch.) Kind of unsettling that the best scene is the one condoning onscreen violence by indulging in it. At least those slave uniforms are stylish. The "son cult" is really clever, with the officers' confusion over sun and son and the message that Christianity will humanize the Empire. This is a contentious notion coming from a secular series. Still, the planet would be interesting to revisit.
Spock Saves the Day: Spock discusses the flaws of Empire with its rulers, and saves Bones in the televised gladiator games.
Oops: Spock really can't fathom the son worship. Uhura figures that out.
Developments: Spock can kick ass! His strength has been demonstrated before, but he's often too bound by his pacifist ideals to take things further than one strike. But throw him in the ring and hey, he can hold a huge, well-trained gladiator dude off with one hand, with weapons he's likely not used before. (Sword and shield.) He also delivers a nerve pinch to McCoy's opponent to save the struggling doctor. Spock later agrees Christianity will be good for the planet, but would sanction the introduction of any philosophy of peace and equality.