Origins and Names
Castamir was of the Dúnedain, the Men of Númenórean descent who held the South-kingdom, and he stood within the House of Anárion, though not upon its direct line. The chronicles of Gondor trace him to Calimehtar, the younger brother of King Rómendacil II, so that his kinship with the reigning house ran through a collateral branch rather than from father to son. This mattered in a realm where the succession had long passed by descent within one house, and it placed him at a distance from the throne that no ordinary reckoning would have closed. The king-list of the Southern Line nevertheless preserves his name in its proper place, counting him twenty-first among the Kings, set between the two spans of Eldacar's reign.
His standing rested less on lineage than on office. Castamir held the command of the fleets as Captain of Ships, one of the great charges of the realm, and his strength lay accordingly among the shipmen and the people of the coastlands and of the haven of Pelargir. There the blood of Númenor was more mingled than in the inland provinces, yet pride in Númenórean descent was no less fierce; among such men Castamir found ready ears. He is remembered as a proud man, whose thought was bound to the sea and to the southern havens rather than to the older seats of the kingdom about Osgiliath and Minas Anor.
The name itself is of the High-elven tongue, as were the throne-names of the Kings of Gondor throughout this age; the contrast is drawn sharply in the annals, where Eldacar is recorded as having borne among his mother's Northern kindred the name Vinitharya before he came to the crown. No gloss of Castamir's name survives in Tolkien's published writings, and it is safer to leave it unglossed than to guess; only its second element answers to the recurring Quenya word for jewel, familiar from many Númenórean names. The addition by which he is best known, the Usurper, is not a title he bore but the judgement of the chroniclers who set down the Southern Line afterwards, and it has followed the name ever since.
The Kin-strife and the Usurpation
The quarrel that carried Castamir to the sceptre had been prepared a generation before he claimed it. Rómendacil II had sent his son Valacar as an envoy to the Northmen of Rhovanion, and Valacar there took to wife Vidumavi, daughter of King Vidugavia, so that the heir of Gondor was born of a mother who was not of Númenórean race and whose people were shorter-lived. Many in the South-kingdom accounted this a debasement of the royal house, and the discontent grew louder as the old king aged, being fed by the fear that the long life of the Kings would fail in the son of such a union. Rebellion was already gathering before Valacar died in the year 1432 of the Third Age, and when Eldacar took the crown it broke into open war. Castamir set himself at the head of the rebels, and to his cause came the shipmen and the men of the southern fiefs, whose pride in unmingled descent gave the rising a colour of principle that its later course did little to keep.
The war ran on for some five years before it was decided. In 1437 the rebel host closed upon Osgiliath and besieged the king within it; the city was fired in the fighting and never wholly recovered from that ruin, and the palantír that had been kept there was lost in the waters of the Anduin, a loss which the chroniclers of Gondor reckoned among the gravest of the age. Eldacar broke out at last and escaped northward into Rhovanion, where his mother's kindred received him, and a good number of his own folk went with him into exile. His son Ornendil did not get away. Taken alive after the fall of the city, he was put to death by Castamir's order, and it is this deed above all others that fixed the victor's reputation; the annals set it down as murder rather than as an act of war.
Castamir held the crown for ten years, from 1437 until 1447, and the record of that decade is short and unfavourable. He is described as harsh and without generosity, quick to shed blood where none needed shedding, and the goodwill that had carried him to victory drained away as the character of his rule became plain. His attention lay upon the fleets and the sea-havens, and he took little thought for the inland provinces or for the lands beyond the mountains; it was reported, and believed, that he meant to move the seat of the kingdom to Pelargir. Nothing was better calculated to lose him Minas Anor and Ithilien, whose people had no wish to become a province of a maritime power, and the party that had lifted him up narrowed steadily to the coastlands alone. Thus the very support that made his rising possible determined the shape of his fall.
In 1447 Eldacar came back out of the North with an armed force, and the Northmen of Rhovanion were not his only strength: men came to him out of Calenardhon, out of Anórien and out of Ithilien, so that what began as an invasion took on the character of a homecoming. The armies met at the Crossings of Erui in Lebennin. The battle was won by Eldacar, but at a cost the chroniclers did not conceal, for much of the best blood of Gondor was spilt on both sides by kinsmen who should have stood together. Castamir himself was killed there, cut down by Eldacar in person, and the annals present the deed openly as the settling of the debt owed for Ornendil. Eldacar took the crown again and held it until his death in 1490, so that his name stands twice in the king-list with the usurper's between.
The death at Erui did not end the matter, and the longest consequence of Castamir's career belongs to the years after it. His sons escaped the rout with a body of kinsmen and shut themselves in Pelargir, where they were besieged; before the city could be taken they got away by sea in the ships that had always been the family's true strength, carrying off a great part of the fleet. In 1448 they seized Umbar and made it a stronghold hostile to the kingdom, and there their descendants held out for many lives of men, so that the great haven of the South passed out of Gondor's keeping and became a base for its enemies. The enmity was long and precise in its aims: in 1634 the Corsairs under Angamaitë and Sangahyando, great-grandsons of Castamir, fell upon Pelargir and killed King Minardil there. The Kin-strife left Gondor weaker in numbers, poorer in loyalty along its own coasts, and, through Umbar, provided with a permanent wound in the South.
Role and Powers
Whatever Castamir could do, he could do through office and through armed men; nothing in the annals credits him with any other kind of strength. The fleets he commanded were the chief instrument of the South-kingdom, built up in the days of the Ship-kings when Gondor's reach along the southern coasts was at its height, and whoever held them held the mouths of Anduin, the great haven at Pelargir, and the passage to the southern seas. That command was the whole of his power, and it explains both the speed of his rising and its shape: he could bring force to bear wherever water carried it, and hardly anywhere else. The chroniclers do not describe him as a captain of unusual skill or as a lawgiver, and the ten years of his reign are recorded without a single measure of government to their credit.
The limits are as plain in the record as the powers. Castamir was a mortal man of the Dúnedain, with no arts and no instrument beyond the sceptre and the ships; no use of the palantíri is attributed to him, and the Stone that had been kept in Osgiliath was already beyond recovery. Nor did possession of the crown make it his. In Gondor the right to rule was reckoned by descent from Anárion, and the office conferred no authority to alter that reckoning, so that ten years of unchallenged tenure changed nothing in the eyes of those who kept the annals. The surviving heir of the elder line stood as a standing claim against him which no act of his own could cancel, and the attempt to cancel it by the killing of the heir's son only fixed the claim more firmly.
In the wider shape of the legendarium Castamir has no part in the long struggle against the Shadow; he appears in no tale of the Third Age proper, but only in the annals of the kings, and his importance is measured entirely by what his rising cost. Appendix A treats the Kin-strife as one of the injuries from which the South-kingdom never recovered its former strength, to be set beside the Plague and the invasions from the East, and it is in that company rather than as a figure in his own right that his name carries weight. He stands, in effect, for the proposition that Gondor's gravest wounds in this age were self-inflicted.
Kin, Faction, and Feud
The record preserves Castamir almost entirely through opposition, and the bond that defines him is his rivalry with Eldacar. What the annals insist upon is that the two men were kin, and the name given to the war says as much; the chroniclers dwell less on the merits of either claim than on the wrongness of Dúnedain shedding Dúnedain blood. Of anything else that might be called a personal tie, nothing survives. No wife is named for him, no mother, no sister; even the sons who outlived him are left unnamed in Appendix A, mentioned only as a body of men who got away. His adherents were bound to him in the same impersonal fashion, joined by a shared grievance about descent rather than by loyalty to his person, and a following of that kind lasts only while the grievance is served.
The enmity outlived both principals and became hereditary on either side. Because the elder heir did not survive the fall of Osgiliath, the crown passed at Eldacar's death to a second son, Aldamir, and it was Aldamir who was killed in 1540 in war against the Haradrim and the Men of Umbar, so that Castamir's descendants had accounted for two of Eldacar's sons across a century. Aldamir's own son Vinyarion defeated the southern peoples in 1551 and took the name Hyarmendacil in memory of that vengeance, which shows how firmly the quarrel had settled into the family reckoning of the House of Anárion.
It ended only with extinction. In 1810 King Telumehtar took Umbar by assault and broke the corsair power there, and the annals note that the last of Castamir's descendants perished in that stroke; the king added Umbardacil to his name, so that the final act of the feud is commemorated in a royal title much as Castamir's own name carries the judgement passed on him. The line he founded thus produced no house and no legacy but its hostility, and is remembered under the name of the men it fought.