The natives of the planet 892-IV were humanoids virtually indistinguishable from Human norms. The culture of 892-IV was considered a prime example of Hodgkin's Law, developing an analog of Earth's Roman Empire and Jesus Christ, about 2300 years after those events transpired on Earth.
At the time of the USS Enterprise visit in 2268, the Roman Empire of 892-IV had yet to fall and a nascent Christianity was only beginning to flourish, in the early modern age of television.
According to Spock, the natives spoke "colloquial English" of the mid-20th century. (TOS: "Bread and Circuses")
According to the novel The Poisoned Chalice, the "Magna Romanii" are humans transplanted from Earth by the Preservers. They are members of the Federation in the late 24th century.