Fantasy realms are generally many types, the sword and magic type, the post-apocalyptic type, the time before, and the time after but no apocalypse. Caranus, in my eyes, is a mixture of a few of those. There is the sword and sorcery, but there is the time before too, and it is also post-apocalyptic. The most significant feature of this last example is the great Orcish Apocalypse.
The Orcish dominance had three stages in Caranus. When the ship transporting the Orcs crash landed in the center of Caranus marks the beginning of the Orc epoch. The ship was a starship, a generation ship of Orcish colonists a million strong on the ship, but the landing was rough and there were quite a number of escape pods that were launched as the ship crashed and only a couple of hundred thousand landed with the main ship. The rest were scattered across the planet, most of them in the vast oceans that covered nearly eighty percent of the surface. Some early escape pods fell to three of the moons that can support life where they mostly died as the lifeforms there are very hostile to most life. The Orcish settlers that scattered quickly had to adapt as there technology failed over a few centuries and their knowledge was inadequate for this type of habitat. Those at landed on Caranus, however, had the advantage of the main ship, which held a vast library of information and some limited advanced technology facilities. They failed too after a millennia, but by then it did not matter.
The Orcs of Caranus rapidly began to dominate the portion of the world they landed in. They quickly encountered some of the native creatures, elves, dwarves, hobbits, gnomes etc; there relations were at first good, superior technology allowed them a position of superiority, but the natives use of magic equalized the relationship somewhat. The other encounters they had with native life went less well, particularly with Dragons. Younger dragons were a curiosity, often a lethal one for orcs unless prepared, and for the dragons if they were. The larger dragons were significantly more dangerous and very quickly they learned that larger hunting parties were necessary or the colony might fail entirely. The very largest Dragons were nightmares capable of destroying even those hunting parties, but the dragons were thankfully very rare. Almost from the beginning a few of the Orcish settlers tried to learn the arcane mysteries that the natives used, the ones that the Dragons seemed to be masters of.
Architecture of this period would be very familiar to city dwelling people of Earth, tall skyscrapers thirty to fifty stories high, and a few much taller, made of aluminum reinforced concrete, these structures can be still seen many millennia after this age. Their roadways stretched a thousand kilometers out from the landing site and are straighter than most arrows.
It took a thousand years for the technology to fail, but fail it did. It failed not suddenly but system by system until in the end the Orcs were completely dependent on native technology and arcane powers. The Middle Empire. The middle empire spread out further, out as far as the first ones did ten thousand years before them. The government was more fractured and they fought among themselves more frequently than they fought to expand and fought against nature. And the Dragons. In this time, the dragons were more of a threat. The architecture of the time started with ten story structures that collapsed after a couple hundred years, before the adopted stone and magically reinforced structures. Road technology was strong still if less straight and less robust, the old empire was still the heart of their holdings, but every other corner of the continent was occupied to one extent or another. Other continents entered a middle empire equivalent much sooner and many entered a lower empire equivalent earlier too.
About five hundred years after the technology failed the Middle Empire failed across the planet abruptly. Catastrophically. Technology that failed did not mean that it was not working. The ship was powered and had engines that wile broken were still working at some small level and they were working quite well when they were being correctly maintained. The Cult of the Machine, as it was known, had rituals that they performed regularly that kept the reactors of the ship in good order for years, but a religious schism within the cult about the importance of one ritual over another ended the Middle Empire. The ships reactor and the, long dormant, drive systems imploded and set off a chain reaction, which ended a carrier wave that was sent to all the escape pods dotted around the star system that caused all of them to explode as well.
The explosions were a twice deadly threat to the world. The ship's explosion ripped the surface off the planet and pushed it into a mountain range in the center of the continent, the blast zone is still uninhabitable to this day. The second component to the catastrophe was more devastating. The radiation that was expelled by the less complete detonations in the escape pods affected everything. Plants were more resistant to the effects as were the non human, and non orcish races, but both were affected. Orcs were affected most, the races of ogres through goblins arose from radiation affected orcs. Humans were affected too, giants and anything like that arose from this event. Hybrid animals like manticore and unicorns arose. Bullywogs and other things like that were also mutations from this event. Disturbingly dragons were also affected. Hydras and others Draconic like beasts arose from this time, juvenile dragons became more like animals and less like dragons and things like Wyverns arose and grew beyond their normal diminutive size. Today the effects of the radiation are minimal, except in the central desert and in the jungles over the shining mountains.