During the Pleistocene, while the people of the Eleven Kingdoms were living as hunter - gatherer tribes, some were born with para-normal abilities. The ordinary people feared them and often cast them out of their tribes. Many died, but some of these misfits banded together and began their own tribe, but they were not welcome anywhere. They might settle somewhere for a while, but eventually they would have to move on. Sometimes because of was climate shifts, sometimes because of harassment from the "normal" humans. In the old tongue, dery, pronounced der-yee, meant place or home. The misfits, therefore, were called Deryni - quite literally The Homeless Ones.
After several generations they found themselves in the Kheldish Riding. In many ways their skills enabled them to survive better, but the constant harassment was taking its toll. There was an island on the horizon north of Kheldor. They loaded rafts and set sail.
West of that island was a chain of volcanic islands curving gently south-southwest. Over the next few years they followed this chain to a large, beautiful crescent shaped island. Mild and fertile they named it Caeriesse, for she was a caress after all the abuse they had faced, and settled there secure from their tormentors.
The wide bay guarded by the northeast and west arms of the island opened southeast. Rugged peaks broke the north wind and left south facing fertile slopes perfect for vineyards. A small spring-fed lake high in the northern hills fed a stream that wound its way through the foothills. Other streams joined this tiny watercourse and swelled it until it reached the central plain where it meandered in oxbows creating fertile parkland supporting a diverse ecology.
A dearth of caves required the refugees develop building skills, and the scarcity of large game resulted in the invention of weaving. Conversely, though, the great variety and supply of plant and mineral dyes encouraged the development of the arts.
The volcanic "stepping stone" islands were an intermittent connection to the mainland at best. Temperature fluctuations and earthquakes would flood or reveal them every few hundred years. Most of the time Caeriesse was completely cut off from the rest of the Eleven Kingdoms.
This isolation led to inbreeding that re-enforced their para-normal talents. Over the generations they developed their talents and created rituals to help channel and control the powers. These rituals were founded on the old gods and elementals, particularly on the four physical elements, air, fire, water, and earth. They also founded scholae and collegia to train their children and research new techniques.
A few rituals also recognized the three esoteric elements, good, evil, and balance, but no institutions were dedicated specifically to these. They were, instead, integrated into the higher teachings of the four main schools. These seven elements comprised the guiding points of all Deryni lore.
Eventually they became accomplished sailors, but only rarely returned to the mainland to trade and raid, never revealing their origin. This tiny amount of contact was enough to bring the concepts of alphabet and zero to their island. It also occasionally brought new people, but only occasionally. It was just enough to keep them from becoming a completely new race.
For thousands of years they lived in peaceful isolation. True they had their share of problems. Some people in every generation would abuse their powers and try to take advantage of others, but each generation dealt with its problems and life went on.
But Caeriesse doom was sealed in its very origins. The great bay was actually the caldera of a huge undersea volcano. The largest and central of an arc of volcanoes beginning in the northern sea, sweeping past the Eleven Kingdoms, and ending deep in the mid-oceanic plain. Only the northernmost cones ever rose above the sea, and only Caeriesse was large enough to support a nation. These islands formed a dotted line weakening the earth's crust. A rift waiting to happen, needing only a trigger.
The world was younger and more active then. Volcanic action far down the chain would send tremors echoing through the tectonic plates. Sometimes a series of quakes would lift an island or two far enough for people to settle, and then, a generation or more later, another series would drop these islands back into the sea. The Caeriesseans learned to read the signs and flee to their main island until the earth again settled.
Perhaps they should have been more suspicious when a series of tremors sank half the western arm protecting their great bay, but Caeriesse herself had always been their bastion. The people could not conceive of a world without her.
Another warning came when a severe earthquake severed the northeastern arm of the island. Now the winter storms had a passage into the great bay and the shining city began to take a beating. But life eventually settled to a new equilibrium.
Deep under the island, though, hidden from those on its surface, all was not well. The bedrock of Caeriesse was a honeycomb of lava tubes. Those on the northern and northwestern sides had long ago succumbed to the pounding surf leaving steep mountain slopes and cliffs behind suitable only for seabirds' nests and seals. The catacombs under the caldera, though, had never faced the full force of the sea.
Over the next generations the sea currents and storms began to take their toll on the basalt foundation of the island. Slowly the walls of the old lava tubes were eroded until they collapsed from the weight above them. The tiny tremors these collapses engendered were minor compared with the quakes of past generations. Caeriesse settled into a happy and prosperous century. But the sea ate away at the island's heart just the same.
Slowly the connective tissue holding the incipient rift together eroded. Silently the sea filled in the gaps its currents and storms created. Like a thief preparing for a major heist, Mother Nature laid her plans. Then as swiftly, but not nearly as quietly, she struck.
An eruption at the far end of the chain sent its tremors back up the line. It didn't take much to break the final connection. The rift formed and Caeriesse began to sink. Within days only the highest peaks remained above water and these had shifted and leaned far in toward the old bay. The gently rolling hills of the southern slopes had become steep cliffs and the steep northern face was now a gentler, almost climbable slope.
Of the Deryni's four major collegia only the Air Seat remained. Mere, Pyre, and finally Geo Seats had flooded or crumbled taking most of their students and teachers with them. Only those few who had happened to be away from their studies and in the highest reaches of the northern barrier mountains survived. Those and the sailors already at sea. Every day more temblors rocked loose the precarious hold of the island remnant. Rough seas and barely hidden rocks made it impossible to bring rescue ships anywhere near the isle. The survivors were on their own. The ships of Caeriesse came as close as they could to the island and waited for survivors to brave the waves on their own.
And brave the angry sea they did. In small boats designed more for the quiet waters of a lake, on rafts barely held together with rope, and even swimming the survivors braved the icy waters. Many died, but many others were pulled aboard ships and ferried to the mainland. The Caeriessean fleet circled between the island and the mainland. Some ships always ready to pull the brave and lucky from the sea, others speeding their way toward safe harbor only to return to patrol again a few days later.
In a matter of weeks it was all over. Caeriesse was no more and the tiny remnant of her population was scattered through the southwest coastal regions of the Eleven Kingdoms. Deryni they were again, but this time wiser and more willing to blend in with the other inhabitants of their new homes.
They learned new religions and incorporated them into their rituals. They also developed the transfer portal. Whenever possible Deryni married Deryni, but in all other ways they blended in with their hosts. Judicious use of their talents allowed them to rise in power, both secular and ecclesiastic. Scholae and collegia were founded and they began to be able to use some of their powers openly. Healing was especially welcome.