The human inhabitants of the planet 892-IV, whose civilisation is a Roman Empire that never fell, complete with slavery, televised gladiator fights and a persecuted faith of the Son.
The people of 892-IV are physically human and speak English, on a world whose history ran parallel to Earth's until Rome failed to fall. Spock cites Hodgkin's Law of Parallel Planet Development. Their technology matches Earth's mid-twentieth century, with motor cars, machine guns and television, but the state is still ruled by a proconsul and built on hereditary slavery softened by pensions and medical care.
They appear in the Original Series episode Bread and Circuses. Kirk, Spock and McCoy find that the merchant captain R.M. Merik has become First Citizen Merikus under Proconsul Claudius Marcus, and are forced into the arena for a broadcast gladiator match.
Runaway slaves such as Septimus and Flavius follow a religion of peace that the landing party takes for sun worship, until Uhura realises they mean the Son of God.