The Aurean Dominate is an empire controlling the entire planet Aurea and a scrap of the neighboring planet Awal (known as the Exarchate of Tifinagh). Aurea is around Earth-sized (although all of the landmass is in the southern hemisphere so it only has maybe 2/3 Earth's land area) and has extremely diverse climates and geography (although the vast majority of the population lives in areas with tropical or Mediterranean climates, and this is true in Tifinagh as well). However, this planet only has around the level of technology that the Eastern Roman Empire had at the time of its final fall in 1453 (with the addition of printing press). Could such an empire control all this massive expanse of territory with this level of technology? Here are a few more bits of context to factor in:
The Aurean Dominate makes use of carrier rhamphos (basically pterosaurs of the Rhamphorhynchus genus that operate in a similar manner to messenger hawks from Avatar: The Last Airbender), cutting down communications times significantly
The Aurean Dominate is much more democratic than most empires, with the Dominus (head of state) being directly elected by the Aurean people, pretty much universal suffrage (among men) throughout the empire, proportional representation in the Aurean Senate, and an independent judiciary. Additionally, each province is more-or-less self-governing provided they do not conflict with federal laws, and each province chooses their own Governor, with some even having completely different systems of government (i.e. Terra Centralis is led by an elected Archon while Tangolia has a hereditary Khan). Each of these governors answers answers only to the federal government and must swear an oath of loyalty to the Dominus. Nevertheless, the aristocracy still wields considerable influence over politics, often using their vast financial resources to bribe politicians or publish disinformation to manipulate the largely uneducated voters (in addition to comprising the vast majority of Aurea's politicians in the first place due to their near monopoly on higher education).
All of Aurea's major settlements are connected by a well-maintained Roman-style road system
Aurea has a professional army of around 500,000 men at any given time, but this can be supplemented by upwards of 2 million conscripts in times of emergency.
In terms of rideable animals, Aurea has access to horses/unicorns, griffins, hippogriffs, pegasi, argentavis, deinonychus, Aurean camels, zebras/quaggas, macrauchenia, toxodon, and Tifinaghian elephants. (For the animals that either do not exist or are extinct in our world, I linked to the media portrayals of those creatures that are closest to what I have in mind).
In terms of overall culture, the main groups are best described as follows in terms of real-world inspiration: ethnic Aureans (the majority of the population) are Romano-Byzantine with hints of Turkish, Andalusian, Minoan, and Spanish Caribbean; ethnic Centralians are more Greco-Byzantine with hints of Mycenaean, Phoenician, and Minoan; ethnic Tangolians are a mix of Mongol, Turkish, Pashtun, and Korean; and Tifinaghians are a blend of Romano-Byzantine and Amazigh/Berber.
Although still uneducated by modern standards, the average Aurean peasant has at least what we would consider an elementary school education and is literate.
One of the most popular things the government does to keep the people happy is the Dole, free wheat, olive oil, and pork for the poorest Aurean citizens (inspired by the Roman grain dole). The vast majority of the supply for this comes from the Exarchate of Tifinagh.