This story is based in the world of Pern by Anne McCaffrey
+Rukbat, in the Sagittarian Sector, was a golden G-type star. It had five planets, two astroid belts and a stray planet that it had attracted and held in recent millennia. When man first settled on Rukbat's third world and called it Pern, they had taken little notice of the strange planet swinging around its adopted primary in a wildly erratic elliptical orbit. For two generations, the colonists gave the bright Red Star little thought - until the path of the wanderer brought it close to its stepsister at perihelion. When such aspects were harminous and not distorted by conjunctions with other planets in the system, the indigenous life form of the wandering planet sought to bridge the space gap between its home and the more temperate and hospitable planet. At these times, silver Threads dropped through Pern's skies, destroying anything they touched. The initial losses the colonists suffered were staggering. As a result, during the subsequent struggle to survive and combat this menace, Pern's tenuous contact with the mother planet was broken.
+To control the incursions of the dreadful Threads - for the Pernese had cannibalized their transport ships early and abbandoned such technological sophistication as was irrelevant to this pastoral planet - the more resourceful men embarked on a long-term plan. The first phase involved breeding a highly specialized variety of a life form indigenous to thier new world. Men and women with high empathy ratings and some innate telepathic ability were trained to use and preserve these unusual animals. These dragons - named for the mythical Terran beast they resembled - had two valuable characteristics: they could get from one place to another instantaneouslyand, after chewing a phosphine-bearing rock (fire-rock), they would emit a flaming gas. Because the dragons could fly, they were able to char Thread in midair, and then escape from its ravages.
+It took generations to develop to the fullest the potential of the dragons. The second phase of the proposed defense against the deadly incursions would take even longer. For Thread, a space-traveling mycorrhizoid spore, with mindless voracity devoured all organic matter and, once grounded, burrowed and proliferated with terrifying speed. So a symbiote of the same strain was developed to counter this parasite, and the resulting grub was introduced into the soil of the southern continent. The original plan was that the dragons would be a visible protection, charring Thread while it was still skyborne and protecting the dwellings and the livestock of the colonists. The grub-sumbiote would protect vegetation by devouring any Thread that managed to evade the dragons' fire.
+The originators of the two-stage defense did not allow for change of for hard geological fact. The southern continent, overtly more attractive than the harsher northern land, proved unstable and the entire colony was eventually forced to move north to seek refuge from Threads in the natural caves on the continental sheild rock of the north.
+The original Fort Hold, constructed in the eastern face of the Great West Mountain Range, soon grew too small to hold the colonists. Another settlement was started slightly to the north, alongside a great lake conveniently formed near a cave-filled cliff. But Ruatha Hold, as the settlemant was called, became overcrowded within a few generatins.
+Since the Red Star rose in the east, the people of pern decided to establish a holding in the eastern mountains, provided a suitable cavesite could be found. Only solid rock and metal, both of which were distressingly short supply on Pern, were impervious to the burning score of Thread.
+The winged, tailed, fire-breathing dragons had by then been bred to a size that required more spacious accommodations than the cliffside holds could provide. But ancient cave-pocked cones of extinct volcanoes, one high above the first Fort Hold, the other in Benden mountains, proved to be adequate and required only a few improvements to be made habitable. However, such projects took the last of the fuel for the great stone-cutters, which had been programed only for regular mining operations, not for wholesale cliff excavations. Sudsequent holds and weyrs had to be hand-hewn.
+The dragons and their riders in their high places and the people in their cave holds went about their seperate tasks, and each developed habits that became custom, which solidified into tradititon as incontrovertible as law.
+Then came an interval of two hundred Turns(Years) of the planet Pern around its primary - when the Red Star was at the other end of its erratic orbit, a frozen, lonely captive. No Threads fell on Pern. The inhabitants erased the depredations of Thread and grew crops, planted orchards from precious seed brought with them, thought of reforestry for the slopes denund by Thread. They even managed to forget that they had once been in grave danger of extinction. Then the Threads fell again when the wandering planet returned for another orbit around Pern, bringing fifty years of attack from the skies. The Pernese once again thanked their ancestors, now many generations removed, for providing the dragons who seared the dropping Thread midair with their fiery breath.
+Dragonkind, too, had prospered during that interval and had settled in four other locations, following the master plan of interim defense.
+The significance of the southern hemisphere - and of the grub - had been lost in the immediate struggle to establish new settlements. Recollections of Earth receded further from Pernese history with each successive generation until memory of their origins degenerated into legend or myth and passed into oblivion.
+By the Third Pass of the Red Star, a complicated socio-political-econmic structure had been developed to deal with recurrent evil. The six Weyrs, as the old volcanic habitations of the dragonfolk were called, pledged themselves to protect Pern, each Weyr having a geographical section of the northern continent literally under its wing. The rest of the population agreed to tithe to support the Weyrs since these fighters, these dragonman, did not have arable land in their volcanic homes. They could not afford to take time away from nurturing their dragons to learn other trades during peacetime, nor could they take time away from proteting the planet during Passes.
+Settlements, called Holds, developed wherever natural caves were found - some, of course, more extensive or strateqically placed than others. It took a strong man to hold frantic, terrified people in control during Thread attacks; it took wise administration to conserve victuals when nothing could be safely grown, and it took extraordinary measures to control population and keep it productive and healthy until such time as the menace passed.
+Men with special skills in metalworking, weaving, animal husbandry, farming, fishing, mining formed Crafthalls in each large Hold and looked to one Mastercrafthall where the precepts of their craft were taught and craft skills were preserved and quarded from one generation to another. One Lord Holder could not deny the products of the Crafthall situated in his Hold to others, since the Crafts were deemed indapendant of a Hold affiliation. Each Craftmaster of a hall owed allegiance to the Master of that particular craft - an elected office based on proficiency in that craft and administrative ability. The Mastercraftsman was responsible for the output of his halls and the distribution, fair and unprejudiced, of all craft products on a planetary rather than parochial basis.
+Certain rights and privileges accrued to different leaders of Holds and Masters of Crafts and, naturally, to the dragonriders whom all Pern looked to for protection during the Threadfalls.
+On occasion, the conjunction of Rukbat's five natural planets would prevent the Red Star from passing close enough to Pern to drop its fearful spores. To the Pernese these were Long Intervals. During one such Interval, the grateful people prospered and multiplied, spreading out across the land, carving more holds out of solid rock, just in case Thread returned. But they became so busy with their daily pursuits that they preferred to think that the Red Star had indeed passed beyond any danger to them.
+No one realized that only a few dragons remained to take the skies and that only one Weyr of dragonriders was left on Pern. Since the Red Star wasn't due to return for a long, long while, if ever, why worry? Within five generations, the descendants of the heroic dragonmen fell into disfavor; the legend of past braveries and the very reason for their existance fell into disrepute