Terminus Est is a sword in the science fiction series The Book of the New Sun by Gene Wolfe. It is wielded by Severian, a torturer and the narrator of the series.
In the Shadow of the Torturer, after Severian is expelled from his guild and the city of Nessus for showing mercy to one of his charges, he is sent north to serve as an executioner in a different city. Before Severian leaves, Master Palaemon gives him Terminus Est. A sharp, intimidating sword, it serves as a symbol of his authority and as a deadly weapon. Despite its utility, the sword is apparently extremely ostentatious, as "art had been lavished upon her," according to the narrator.
Terminus Est is described as being "Light to raise, weighty to descend." This is due to (in addition to the obvious ethical quandary, in that raising the sword causes no harm, but the descending stroke ends a life by decapitation) a channel in the spine of the blade, containing liquid hydrargyrum, another name for mercury. (Wolfe makes use of obscure terms from Latin and Greek in many of his works, and in the New Sun Cycle additionally makes heavy use of French and Spanish.) Given the fact the novel's text is described as having been translated from "a language that has not yet achieved existence", the substance referred to may not in fact be mercury, although its properties would seem to suggest that it is. The channel would have been extremely difficult to fabricate: the usual techniques of forging would have crushed it. However, a simple possibility is that the sword was forged and then the channel drilled, especially before quenching and heat hardening.
In addition, the melting point of iron is 1811 K (1538 °C, or 2800 °F), which is far above the boiling point of mercury (629.88 K, 356.73 °C, or 674.11 °F), which would complicate the task of sealing the mercury into the channel. Terminus Est is mentioned several times in the book as being able to be removed from its hilt, and especially after it is destroyed, Severian removes the shards from the hilt and keeps the furniture. This indicates a Japanese style of construction with hilt independent of sword tang. A simple means of sealing the mercury into the sword would be to employ a plug or screw in the end of the tang. This could easily be hammered over once inserted so that the edges of the tang overlap and trap in the plug. All of this would be covered over by the sword furniture and could have been accomplished with well-below-modern levels of technology.
During the course of Severian's travels Terminus Est plays a vital role, alternately saving his life and placing it in peril. Shortly after leaving the Citadel of Nessus, Severian is caught in a ploy masterminded by Agia and her twin brother Agilus, designed to deprive him of his sword and belongings after he loses a duel to the disguised Agilus. Terminus Est is described as having been one of the last works of a famous swordsmith—so in addition to its inherent utility, it is also an antique; Agia describes it as being worth ten times the value of her shop and its inventory.
The sword is double-edged, having both a "male" and "female" side, designed to sever only male heads with one edge and only female heads with the other. Severian takes meticulous care of the sword, always cleaning, oiling, and sharpening the blade before and after an execution, to the point where he uses Terminus Est to shave with, forgoing a razor.
It is analogous to a real-world Sword of Justice, which is designed solely for the purpose of execution. Just like this sword, Terminus Est has a square end and therefore cannot be used as a thrusting weapon.
Terminus Est is eventually destroyed while Severian wields it in battle. This occurs during his fight against Baldanders, his former traveling companion. When Terminus Est strikes the massive and bizarre mace Baldanders wields, which seems to be tuned to the resonance frequency at which Terminus Est would shatter, both weapons are destroyed. Upon the destruction of Terminus Est, Severian recovers the hilt of the shattered blade, later returning it to Master Palaemon upon his triumphant return to the Citadel at the close of the series.
Terminus Est is commonly translated from the Latin as "This is the end", or literally "It is the end." It can also mean "this is the limit", "this is an end" (due to the lack of the definite article), or "this is the border". However, Severian interprets the phrase to mean "this is the line of division," and Typhon translates it as "this is the place of parting."
While it is not strictly in accordance with the grammar of the original Latin, it might perhaps be considered appropriate by some to rephrase the translation "This is the end" as "It is finished." This adjustment would provide a further nod to Christian symbolism, as in the section below.
Severian describes Terminus Est several times as a "paterissa" or cross (the sword has long, straight guards and is carried over the shoulder, tip-downward) and once as an "iron phallus" (an image suggested by the fluid-filled channel inside the blade.) The cross is of course an instrument of torture and death, but in Christianity it symbolizes resurrection. Master Gurloes's iron phallus was also a torture instrument, but phallic images have long been used to symbolize fertility and therefore life.