The Norse people did not actually refer to themselves as Vikings as an ethnic or national identity. Viking was a profession and was the term for the act of raiding across the sea or a person participating in such an activity.

The name "Ragnar" means "keeper of the fort."

Ravens appear prominently in the series. Ravens had great cultural and religious importance in ancient Norse society, as they were seen as the agents of Odin who was said to own two ravens: Hugin (meaning "Thought") and Munin (Memory) who flew around and gathered information for him. One of Odin's many nicknames is Hrafnaguð, which means "Raven God". Vikings would carry banners depicting ravens. Ragnar's forces carry such banners. As such, the pagan characters in the series are likely to believe that when ravens appear, they are watched by Odin.

The detail that the Norsemen were tattooed is not necessarily speculation. Eyewitness accounts from the Viking Age report that Vikings were, indeed, tattooed. This was also a feature of Celts and Slavs, supporting the idea that the practice was widespread in Pagan Europe.

The women in the opening credits are supposed to be the 9 daughters of Rán, the personifications of the waves. The title sequence is supposed to show the separation of a viking from the living, with the ornaments of his life (gold and weapons) floating down around him. During the shot of the rolling thunder there is a single frame showing Hel Lokisdottir: the goddess of death.

Rollo's tattoo depicts a scene from Norse Mythology: The wolves Hatí and Sköll (the sons of Fenrir) chase the sun and the moon.

Gustaf Skarsgård assisted some of the other actors in the pronunciation of certain Scandinavian words. According to him the word the English speaking actors found most difficult was the name "Knut", which is often anglicized as "Canute" in history books and fiction. In Swedish and Norwegian Knut sounds like "Knuut".

Clive Standen and Gustaf Skarsgård both auditioned to play Ragnar. Travis Fimmel auditioned to play Rollo. Fimmel wanted to play Floki.

According to the sagas from which this series takes some of its plot, Ivar the Boneless was the oldest son of Ragnar by Aslaug.

When Marco ilsø (Hvitserk) and Alex Høgh Andersen (Ivar) were cast in the series they weren't allowed to tell anyone, so they wrote to each other that they didn't get the role.

In scenes involving large groups of Norsemen, the voices in the ambiance are speaking Icelandic, Danish, Norwegian and Swedish.

The first season has nine episodes. 9 is a very special number in Norse Mythology: Odin hung upon Yggdrasil for nine nights to learn the secret of the runes, there are nine worlds in the world tree, Heimdall has nine mothers, Odin owns a ring which creates nine new rings every night, Ran has nine daughters embodying the waves of the sea, there are 9 great lindworms (dragon-like serpents), every ninth year nine males of every species are sacrificed to the gods, Freyr had to wait nine nights until he could marry Gerd, the valknut symbol has nine points, Thor will walk nine steps before dying after killing Jörmungandr, Odin broke free and killed King Geirröd on the ninth night of his captivity and Odin knows 18 (9x2) rune charms.

Jarl Borg was originally a Swedish jarl and Horik would send Ragnar to Sweden to settle the dispute. When Gustaf Skarsgård read the script he wrote to Michael Hirst and informed him that 1) "Sweden" did not exist during that time and 2) Uppsala would most certainly be part of it. Hirst changed it to Götaland (Land of the Geats). Sweden was formed as a consolidation of Götaland and Svealand (Land of the Swedes) where Uppsala is located. While it's very uncertain on what exact date "Sweden" was formed (Götaland and Svealand ruled under a single king is commonly set as a point) the term would not have been used in the time of the Vikings.

"Loðbrók" is not a family name but a nickname meaning "hairy-breeches", presumably from a habit of wearing fur leggings. Vikings often acquired colorful nicknames derived from personal habits, characteristics or traits. The sagas and histories of Vikings are populated with such figures as Helgi the Lean, Ketil Trout and King Harald Finehair (formerly Harald Shag-hair).

Travis Fimmel (Ragnar) is only 13 years older than Alexander Ludwig, who plays his son Björn. Katherine Winnick (Lagertha) is only 15 years Ludwig's elder. This however is in keeping with the Viking era when adulthood was considered to be puberty, therefore marriage at a young age was not just common, but the norm. Women often died in childbirth and the widowed husband would then take another wife of 12 or 13 years of age even if he was an "old" man in his 40's.

There is almost no evidence of what haircut the Vikings wore other than beards for the men and ponytails for the women (based on contemporary Norse art). Therefore the haircuts of several of the Vikings were designed so that hair would not stick out beneath a helmet so enemies would not be able to grab a hold of their hair from behind.

According to Katheryn Winnick the accent of the Norse men is based on Swedish accent.

Composer Trevor Morris has stated he was not really satisfied with the score until he discovered Norweigan musician Einar Selvik and involved him to provide Norse lyrics and authentic instruments used in the viking age on the score. Then he found the unique sound he felt the show needed.

The name of the fictional town of Kattegat is an anachronism. The name itself refers to a strait between Denmark and Sweden. It is derived from Danish words kat (cat) and gat (hole, gate), a lingo for a strait so narrow that a cat would have problems fitting through. This term was coined in 15th century some 600 years after the narrative of the show. The area was known as Norwegian sea or Jótlandshaf (Jutland Sea) during the time of Ragnar and his sons.

The show takes its premise and basic plot from the Icelandic sagas Ragnars saga loðbrókar (The Saga of Ragnar Lodbrok) and Ragnarssona þáttr (Tale of Ragnar's Sons). Some have suggested that the actual protagonist of the cycle is Aslaug. Lagertha does not appear at all in the sagas. She appears in Saxo Grammaticus Gesta Danorum (which is also the basis of Hamlet). Most scholars agree that while there is some historical basis for Ragnar, the father of Björn Ironside and Ivar the Boneless and the plunderer of Paris, Lagertha seems to be entirely made up by Saxo and drawn upon various mythological characters, amazons and shieldmaidens.

The nickname "Loðbrók" refers to a saga about Ragnar that Saxo wrote. In the story, Ragnar dresses himself in a fur coat and fur pants and walks through icy water in order to get the fur frozen. This is to be shielded from two Lindormar (mythical serpents) that have trapped a maiden in her house. Afterwards, the maiden's father mocks Ragnar for having "fuzzy pants", i.e., "Loðbrók".

The distinctive jewelry pieces used in the show were all made by hand by a South Carolina artisan called The Crafty Celt. The Crafty Celt has been researching Viking Era and Early Celtic jewelry for more than a decade.

Ivar the Boneless was a real historical figure. The Vikings had a habit of sometimes giving ironic or teasing nicknames. Ivars nickname 'Boneless' may be referring to the fact that he sailed far(England and up the Russian rivers) and therefore never walked anywhere. In Scandinavian languages the same word is used for legs and bones so the English translation of Ivars' name could be both 'legless' and 'boneless'.

The runic inscription on King Horik's sword is a mix between the Elder Futhark (proto-norse writing system) and the Younger Futhark (old norse writing system). The inscription reads: "Shard af Kings".

The symbol on the shields used by the warriors of Hedeby are two "Fe"-runes - a letter used by Germanic peoples in the dark ages equal to the Latin letter "F" - laid back to back to look like a tree. This is a highly symbolic design as carving several runes into another, a "bindrune", was supposed to summon the magic of the rune. In this case "Fe" symbolizes wealth.

The carved beast heads seen on the prow of the viking longships were there to scare the spirits of hostile lands. Vikings were more than willing to fight the people but did not want to suffer at the hands of hostile spirits, nor did they want the spirits aiding their enemies. Although not shown in this series, they were not always dragons - they could be wolves/ravens etc. They were also removable and would have been taken off when approaching home so as not to scare the friendly spirits as this could bring ill health, a bad harvest or other such bad luck. A more modern equivalent would be a battle flag carried at times of war but not of peace - if you saw a longship approaching with beast head in place, you knew their intentions were hostile.

The colors on the flags and shields of Harald Finehair are red and yellow. These are the colors of the royal house of Norway.

The opening title music from Vikings "If I had a heart" by Fever Ray also featured in Breaking Bad (S4 E3) also at the end of Person of Interest S1E15

Rollo was originally written to be Ragnar's cousin.

The series was originally meant to be called "Raid"

The historical Aethelwulf's first son by his first wife Osburh was named Aethelstan. Athelstan ruled as king of Kent from 839 to his death in 852.

Tadhg Murphy, who plays Arne, lost his right eye at a accident as a self made arrow hit him (He was 13 years old). While his first rehearsal for the show he ask Michael Hirst if he should take his eye out for it. Hirst was really perplexed, because he didn't know that Taghd really is "One Eyed"! He saw the actor the first time with his eye patch, which he wears in the show. In an interview after Murphy wasn't in the show anymore, he revealed that he was asked "thousand times" a day to take his eye out and that bothered him.

Jennie Jacques who plays King Alfred's mother, Judith, is only 10 years older than her on-screen son, Ferdia Walsh-Peelo.

The title of a Saxon nobleman was 'Earl' which comes from the Old English word 'oerl' meaning a 'man of position'. This was the only Anglo-Saxon title retained by the Normans and is the equivalent of a 'European' count.

The word Viking was first used by the Anglo-Saxons some time between the 9th and 10th century, and it is uncertain what meaning they gave to the word. Viking appears three times in the Anglo-Saxon Chronicle in contexts that translate to either robber or pirate, but also appeared in Old English poems like the Battle of Maldon where 'wikingas' was synonymous with sailors. Scandinavian raiders, Vikings to the modern audience, were not called Vikings at the time, however, but instead called Northmen, Pagans, Heathens, or most often Danes. Raiders in Scotland and Ireland were often referred to as Norse. The Scandinavians themselves saw themselves as distinct groups, referring to one another as inhabitants of certain regions; men of Jutland, Vestfold, Hordaland etc. It is a modern idea, encouraged by German nationalism in the 1930s and 40s, that these Scandinavians could be treated as a single homogeneous group. Vikings is a word that carries modern connotations and doesn't distinguish these different groups within Scandinavia, so it is often avoided as term by historians and archaeologists alike.

Ivan Kaye who plays the Saxon King Aelle in this show says his Russian ancestors claimed to be descended from the Vikings.

Harald vows to not cut his hair until he has married, yet his hair get significantly shorter between season 4 and season 5 when he finally cuts it.

Rollo was based on a real Viking called Hrolf (latinized as Rollo) who went on to conquer parts of France. Those parts are now known as Normandy: "Land of the Norsemen". Hrolf was the ancestor of William the Conqueror. Actually being William's Great-Great-Great Grandfather.

Harbard means "Greybeard". It was a nickname of Odin.

In this series Ivan Kaye plays King Ælla. In 'Hammer Of The Gods' (2013) he played Ivar the Boneless, the viking who killed Ælla.

When Ragnar explains his plan to reinvade Paris, he says they need to protect their heads, and he takes a horn that he was holding and puts it up against his head to look like the stereotypical Viking headwear found in re-imagined depictions of Norse warriors by Victorian artists of the 19th century and pop-culture. There is no historical evidence that Norse warriors ever wore horned helmets.

The historical king Horik of Denmark was killed by his nephew Guttorm after the latter had been driven into exile by the former, and become a successful viking.

England is mentioned several times during the series, including by Saxon characters such as Athelstan, Ecbert and Aella. England however did not exist as a concept until the reign of Ecbert's grandson Alfred the Great, and not as an entity until the reign of Alfred's son Edward the Elder. Until this time the area that is now England consisted of the Saxon kingdoms of Wessex (the south), East Anglia (the east), Mercia (the midlands), Northumbria (the North) and the (celtic) British Kingdom of Kernow (Cornwall). Until the coming of the Vikings which necessitated alliances these kingdoms were more often than not hostile to each other.

The series makes several references to the medieval text "Egils saga", an account of the life of the 10th century poet and viking Egill Skallagrímsson. Arne's violent death at the hands of Rollo is taken from an episode where Egill is berserker rage pierces an enemy and lifts him high into the air. Ivar's first killing is taken word for word from an event in Egill's childhood, where Egill kills an older boy over a ball. The song Harald Finehair and his men likes to sing is a slightly modified version of a poem composed by Egill. This is an anachronism as Egill was a contemporary of Erik Bloodaxe, the son of Harald. This is also ironic as "Egils Saga" states that Egill and Erik where archenemies. The truth of this is not known as the saga was written more than 200 years after Egill's death and the only contemporary evidence of his life is his poetry. However, one of these poems is the infamous "head-ransom"-poem where Egill asks for Erik to spare him.

Alicia Agneson (Freydis) revealed on Sverigesradio the strangling scene in season 5 episode 20 wasn't simulated. She wanted the scene to look as realistic as possible and was taken care of by a paramedic on set and co-star Alex Høgh Andersen (Ivar The Boneless) despite originally being advised against it by the crew due to the risks.

The final episode for the fourth season, featuring the death of King Ecbert, aired on the same day as the birthday of Ecbert's actor, Linus Roache.

Tadhg Murphy (Arne), Jonathan Rhys Meyers (Bishop Heahmund), Greg Orvis (Siegfried), John Kavanagh (Seer), and Ian Beattie (King Brihtwulf) all appeared in Oliver Stone's Alexander (2004). In Murphy's case, it was his first credited role, as a dying soldier named Glaucos. Coincidentally, Arne and Glaucos both die from spear wounds.