Due to its complexity, Tolkien's legendarium is a subject of studies of various levels by secondary authors and analysts. Some parts of the legendarium also can be subject of misunderstandings by the readers and other misconceptions popularized by the authors and fanon works.
This is a list of many such mistakes circulating in fandom and internet forums more or less like "urban legends", and their refutation.
Definition of First Age; Third Age "of the Sun"
- The First Age began with the first sunrise over Middle-earth and the events of The Lord of the Rings took place in the Third Age of the Sun.
- Actually, Tolkien never described his ages as being linked to the Sun and specifically wrote that the "First Age of the Children of Ilúvatar" began with the Awakening of the Elves, long before the first sunrise. Despite this, many fans believe the 'Ages of the Sun' version is correct because it has been repeated so often. For example, it is found in Tolkien: The Illustrated Encyclopedia by David Day, whose books are generally considered unreliable by Tolkien scholars on the internet such as Conrad Dunkerson and Steuard Jensen.
The Arkenstone was a Silmaril
- The Arkenstone was a Silmaril, probably the one thrown into a fiery pit by Maedhros, and found its way (geologically?) to the north, to be rediscovered by the Khazad of Erebor. Tolkien wrote that the two lost Silmarils would remain lost until the end of Arda. However, in a partial translation of early Silmarillion texts into Old English Tolkien used the etymologically related term 'Eorclanstanas' ('holy stones') to translate 'Silmarils' - suggesting that he may have borrowed the name and other concepts from the Silmarils in describing the Arkenstone.
Elrond visits Elros in Númenor
- Late in the life of Elros his brother Elrond visited him in Númenor and was shocked to see how old he had grown, having chosen the mortality of Men.
- An obscure note published in The Lost Road and Other Writings implies that Tolkien considered the possibility that Elrond and Elros originally sailed to Númenor together and that Elrond later returned to Middle-earth. However, there is no reference in Tolkien's writings to Elrond visiting Elros in his old age.
Arwen, the lastborn of the Elves
- Arwen was the last Elf born in Middle-earth.
- This concept derives from being the youngest Elf whose birth is mentioned in the Tale of Years, and perhaps from publicity for the films; but is never stated in the films or the books.
- Legolas is 2931 years old during the War of the Ring, and thus was born in T.A. 87.
- This information also comes from film publicity and is never stated in the films or books. It may derive from the fact that Aragorn was born in the year T.A. 2931. The date of T.A. 87 for Legolas' birth agrees with another common fan theory, namely that Legolas was born during the period of peace at the beginning of the Third Age. Tolkien, never wrote about Legolas' birthdate.
Legolas hair color
- Legolas is blond.
- This is a visual tradition dating back to the works of the Brothers Hildebrandt in the 1970s and followed in both the animated and live action LotR films. However, Tolkien never specifies Legolas' hair color (although The Hobbit mentions that Thranduil, Legolas' father, was blond). Legolas' hair color is one of the most enduring controversies in Tolkien fandom.
Names of the Nazgûl
- The names of all nine Nazgûl are known: Er-Murazor (the Witch-king of Angmar), Khamûl, Dwar of Waw, Ji Indur Dawndeath, Akhorahil, Hoarmurath, Adunaphel the Quiet (female — see below), Ren the Unclean and Uvatha the Horseman.
- In fact Tolkien recorded the name of only one Nazgûl: Khamûl, the Black Rider who barely missed catching the Hobbits at Bucklebury Ferry. Even the personal name of the Witch-king of Angmar was not given by Tolkien, although some fans refer to him as "Angmar". The names for the eight Nazgûl other than Khamûl which some fans think were coined by Tolkien were actually invented for the Middle-earth Role Playing game (MERP) published by Iron Crown Enterprises (ICE).
A female Nazgûl
- One of the nine Nazgûl was female.
- This concept also comes from MERP. Tolkien's texts seemingly contradict this idea with their consistent references to the Nazgûl as "Men" and "kings", although it could be argued that "Men" includes women and "kings" includes queens. Unsurprisingly, the film version of The Fellowship of the Ring contradicts this idea by showing all nine Nazgûl as men when they received their Rings of Power.
- The name of Legolas' mother is known.
- In fact a name was coined for her for MERP, but never by Tolkien.
The War in the North
- The War of the Ring included a "War in the North", which involved fighting in Eriador and around Rivendell.
- This has been stated as fact by the writers of the films in a DVD commentary and has formed the basis for parts of the 2006 computer game The Lord of the Rings: The Battle for Middle-earth II. However, although Tolkien mentions violent incidents around Bree during the War (not to mention the Scouring of the Shire), no extensive military campaign in Eriador is mentioned in the Tale of Years in Appendix B of The Lord of the Rings. Since the Tale of Years does mention the Battle of Dale and the fighting around Lothlórien, it is clear that it would also have mentioned the "War in the North" if it had been part of Tolkien's conception. Moreover, the section of Appendix A on the Dwarves includes comments by Gandalf to the effect that extensive, destructive fighting in Eriador was averted by the death of Smaug and the Battles of Five Armies and of Dale.
The shape of Middle-earth
- The whole continent of Middle-earth resembles Europe with respective continents for Asia and Africa, while Valinor is in the place of the Americas and has a crescent shape.
- This derives from The Atlas of Middle-earth, which tried to composite a map of Arda based on a drawing by Tolkien (made in the late 1930s or early 40s and published in The Shaping of Middle-earth) and the later well-known maps of Beleriand and the coasts of Middle-earth. Although this old map generally fits the descriptions of the canonical Silmarillion, it is a matter of debate whether earlier concepts of Tolkien's can be used to fill the gaps of later works such as LotR. The Central American coastline does look somewhat like a crescent, but it is unlikely that Tolkien was influenced by it in choosing the shape for the shores of Valinor.
- Hobbits have huge feet.
- Tolkien wrote: "their feet had tough leathery soles and were clad in a thick curling hair, much like the hair of their heads". The idea that they have very large feet, as depicted in the movies, probably derives from illustrations by the Brothers Hildebrandt.
- Déagol is Sméagol's cousin.
- Tolkien only calls him Sméagol's friend in The Lord of the Rings, though in The Letters of J. R. R. Tolkien he writes that Déagol was "evidently a relative (as no doubt all the members of the small community were)" of Sméagol’s. This misconception probably dates from The Complete Guide to Middle-earth by Robert Foster and Tolkien: The Illustrated Encyclopedia by David Day. 
- Sméagol was born in the year 2430 of the Third Age, found the Ring on his 33rd birthday in 2463, and thus was 589 years old when he died in 3019.
- 33 is the age a Shire Hobbit becomes officially an adult. Sméagol "found" the Ring on his birthday. The filmmakers evidently decided that the day Sméagol found the Ring was his 33rd birthday. However: Sméagol was not a Shire Hobbit, but a Stoor, and these had different customs - Tolkien states that the Stoors of Rhovanion received, and did not give gifts on their birthdays (in Unfinished Tales, The History of Middle-earth and Letters); and T.A. 2463 as the date of the discovery of the Ring is an approximate, not a precise date. Thus, there is no exact indication of Gollum's age in Tolkien's books. See http://www.theonering.net/movie/char/smeagol.html
Tengwar on Sting
- The Sindarin words Maegnas aen estar nin dagnir in yngyl im are engraved on the blade of Sting. The worlds translate as "Maegnas (Sharp-point) is my name, I am the spider's bane".
- The origin of this inscription is the depiction in the movies. In the books, Tolkien describes Sting as a rather plain weapon with a simple leather sheath. Unlike Glamdring and Orcrist, it bears no runes for Elrond to translate in The Hobbit. It first receives a name from Bilbo Baggins after he uses it against the giant spiders of Mirkwood.
Saruman, the creator of Uruk-hai
Saruman is believed to be the creator of the race of Uruk-hai (Uruks), the larger, stronger breed of Orcs. This is visualized in The Lord of the Rings: The Motion Picture Trilogy which further established this view. The movie also established wrongly that "Uruk-hai" are a stronger race of Orcs, while in reality it is simply a Black Speech term for the Orcs proper themselves (excluding the Snaga).
The misconception originates from the fact that Saruman perhaps created a race of Orc-men or Men-Orcs in his service. However these aren't the same as the Uruk-hai.
Dorwinion was only mentioned in passing until it appeared on Pauline Baynes' 1969 map, where it was placed on the western shore of the Sea of Rhûn. But contrary to popular belief, it's location was not decided by Tolkien, but by Baynes. Tolkien had asked her to place several locations on the map, but did not specify the location. Baynes picked the location, and Tolkien agreed, though it was not the location he originally had in mind - several references to it place it in "the South". Christopher Tolkien later commented:
- "Dorwinion is marked on the decorated map by Pauline Baynes, as a region on the North-western shores of the Sea of Rhun. It must be presumed that this, like other names on that map, was communicated to her by my father, but its placing seems surprising."
- ― 
It is thought that Middle-earth is a utopia with no finance based economy.
- This misconception is noted by Robert Foster. The misconception originates from the very few times any transactions or the word "money" are mentioned in The Hobbit or The Lord of the rings; most mentions of wealth are vague or in the form of gold or treasures. However in Bree both golden pieces and silver pennies appear. Furthermore, in a draft of "The Appendix on Languages" published in The Peoples of Middle-earth some details of the coins of Gondor are given.