As Commander Spock, science officer of the USS Enterprise, noted, it was a M-class planet with a striking resemblance to Earth. However, as much as there were similarities, there were differences. The land/water proportion, density (5.5g), and atmosphere (78% nitrogen, 21% oxygen) were exactly like those on Earth. However, unlike Earth, the diameter at the equator (7917 miles) and layout of the continents were different. (TOS: "Bread and Circuses")
By the mid-23rd century, the planet had reached the development of Earth's 20th century. Technology included radio communications, road system and powered transportation (such as the Jupiter 8), but no atomic power. Gladiator games became televised. With each century even slaves received rights to medicine and government payments in their old age; the Empire eventually managed stopping rebellions and even wars for 400 years achieving stability.
The Romans believed in a pantheon of gods, but a nascent movement known as Children of the Son, a parallel to Christianity on Earth, started to be embraced by gladiators, slaves and even Senators, disrupting the stability of the conservative Empire.
In 2262, the Federation class 4 stardrive survey vessel SS Beagle was badly damaged by a meteor in the system and a landing party beamed down to obtain iridium ore for repairs. The party was met by the locals, led by Proconsul Claudius Marcus who considered it potentially ruinous to his highly conservative society if word of its existence should be carried elsewhere; the officers were regarded as captured barbarians and forced to fight as gladiators. The Captain R.M. Merik however became First Citizen.
Captain James T. Kirk and the crew of the Enterprise visited the planet 892-IV six years later, on stardate 4040.7, after investigating the debris of the Beagle. They were held captives both by fugitives and later the proconsul, and Merik. The Enterprise managed to escape and speculated that the new religion might bring the transformation of the Empire, much like Christianity did to the Roman Empire. (TOS: "Bread and Circuses")
892-IV had several oceans and at least three continents. It was politically subdivided into a number of provinces.
This planet was described in the The Worlds of the Federation as being very similar to Earth, to the point that the shape of its continents and other planets of its solar system were nearly identical. Both the original and the remastered version of "Bread and Circuses" showed a very different continental arrangement. This work established the indigenous name of the planet as Magna Roma.
According to Star Trek: Star Charts, FGC-892 IV was the fourth planet in the FGC-892 planetary system. The official name of the government was the Roman Empire. It was a non-aligned world that hadn't yet become warp capable. Planetary capital was Rome. The dominant species were the humanoid citizens and barbarians. In 2378, there were an estimated 8.6 billion people living on the planet. The society's technology was nearly equivalent to the mid-21st century on Earth. (pg. 54)