In my world, there was a huge empire spanning across several large continents. It was ruled primarily by a royal family with a number lower ranked governors to look after the individual states.
Looking back though, I realised this might not be that realistic. The Roman empire fell at its peak in around 500BC due to a large amount of reasons - one of them being that the empire was simply too large to sustain itself, the size making communication extremely difficult. The huge population was in constant demand for food and water, and there simply wasn't enough to sustain it. The size also made it difficult to keep the people under control. It was extremely difficult to march troops to defend the outer regions of the empire since it was so extensive. The empire I had was at least double the size of Rome.
To clarify - the empire lies inside a fantasy world. The heart of the empire is within a valley, with mountains surrounding the area on three sides. The civilisation spreads across about three land forms in total - one of them being a small chain of volcanic islands(similar to Indonesia or Hawaii), not far off from the other two continents. Although there aren't any modern communication methods, transportation or technology, this empire has a specific breed of small falcon-like birds who could fly around 150km/h for relatively long periods of time without breaks - generally used for communication, although sometimes horses and messengers are used. The road systems are not unlike Rome's, being quite efficient and can easily sustain the population. Chariots are the fastest method of transportation. The royal family, although not corrupt, are rather impulsive and inconsiderate, and are known for making decisions that affect the society greatly later on. There is a simple empress.
The empire is entirely self sustained - in fact, most of the inhabitants believe that they are the only civilisation in the entire world. (There are in fact others, but they are too far away.) The island chains are generally used as farmlands and livestock farms to sustain the population. Rivers run through the two larger continents - two, smaller rivers through the second continent - one eventually leading to a waterfall which cuts into the ocean - and two small rivers in the first continent, with one large one sustaining the heart of the empire.
This is my first question on here, so apologies if this isn't fully done to standard. Thank you!