Norse mythology’s name often leads people to believe it was a religion exclusively practiced by the Vikings living in the Nordic region.
However, when other religious beliefs, such as Germanic, Celtic, and Anglo-Saxon mythologies, enter the picture, determining the origin of the Nordic religion becomes quite complicated.
Norse mythology originates from the Northern Germanic peoples who lived in what is now the Black Forest in Germany.
This religion spread and changed between prehistoric and modern periods as it traveled across seas and assimilated with other religions, such as Christianity.
Norse mythology’s origins are still murky to archaeologists and historians, but it is clear that Norse beliefs stem from a family or theologies related to the old Germanic religion.
However, Norse religion likely began far before its pantheon included Freyja, Odin, and Thor and was likely a true religion before the Viking Age even began.
Also, see What Is the Norse Creation Story? to learn more.
Did the Vikings Create Norse Mythology?
Firstly, it’s worth noting that although this article uses the term “religion” to describe the spiritual beliefs of the Scandinavians and Germans, before the advent of Christianity, there was no word that meant religion.
Instead, the spiritual beliefs of the Germans, Scandinavians, and even the Romans, were just a part of everyday life.
They would not have seen their mythologies, gods, and beliefs as anything separate from other practices — their spiritual beliefs were ingrained into their politics, activities, and habits.
With that said, the following are the origins of Norse mythology.
The Vikings did not create Norse mythology. Norse mythology is a division of Germanic religious belief, and it was predominantly practiced in Norway, Sweden, Denmark, Iceland, and Germany.
While it is unique to Viking nations and was practiced by many Vikings, it is an evolution of Germanic belief.
Though Norse Mythology was practiced during the Viking Age, evidence suggests that it existed long before that.
However, creating a definitive date for the development of the unique Norse mythology is impossible with the limited evidence scholars have.
What they do know is that Norse mythology is very similar to Germanic mythology.
The pantheons include parallel gods, they have an almost identical world origin story, and they include similar modes of worship.
However, from the Bronze Age to the Roman era, the division between Scandinavia and the new Roman province of Germania left room for Norse mythology to develop a unique identity.
This gradual shift is also evident in the development of unique Scandinavian languages, the Viking Age worldview, and the Scandinavian emphasis on travel and the sea.
On the other hand, Germanic mythology and religion reflected new ideals as the tribes therein entered the Roman Empire and became one unified province under Rome.
When Did the Norse Religion Start?
The Norse religion likely started in the prehistoric era, though the best evidence for the religion is from the Nordic Iron Age, circa 800 BC to 500 AD.
Though textual evidence of the Norse religion dates much later, archaeologists have found early depictions of gods such as Tyr, Odin, and Baldr.
The Norse religion did not start suddenly one day, nor did any known text or event inspire it.
Instead, Norse mythology and religion evolved, transitioning from the prehistoric to the medieval period with marked changes. 
Accounts of Norse Mythology in the Roman Period
Much textual evidence from practitioners of the Norse religion is gone — otherwise, it never existed.
However, scholars can piece together information about Norse religion and mythology from Roman accounts of Germanic religion in the 1st century AD.
The earliest literary evidence of the Germanic religion is from Tacitus (circa 98 AD), who wrote about the religion of the Germanic people in De origine et situ Germanorum (On the Origin and Location of the Germans).
Still, for the most part, Romans attempted to understand the religion through rough analogies. 
They compare Germanic gods to Roman ones, noting features of the people that seemed peculiar to them, putting Germanic religion in Roman terms, and often, giving tribes arbitrary names that the Germanic people would never have called themselves.
For example, Tacitus writes, “Mercury is the principal subject of [the Germanic peoples’] adoration.”
Based on the characteristics of this god, historians have supposed that this Mercury figure is Odin, who shares slight characteristics with Mercury, but is far different upon closer investigation.
Thus, through Roman literary evidence from the turn of the millennium, a very blurry picture emerges of Germanic mythology and an even more blurry account of Norse mythology.
The Earliest Evidence of the Norse Religion and Mythology
The earliest evidence of Norse religion and mythology stems from art and artifacts, such as:
- Stone inscriptions
- Burial goods
Iron and bronze age artifacts such as the large wooden Broddenbjerg idol, the Trundholm Sun-Chariot, and the Vikso Helmets place Norse religious practice as far back as 1800 BCE. 
However, these artifacts do not directly correspond with the Norse mythology most people would recognize today.
From archeological finds, scholars can trace Norse religion back to the prehistoric period as a solar-centric practice that believed that the sun was drawn across the sky by a chariot — a feature very common to many ancient religions.
Likewise, wooden idols were common in this era.
Although few survive, many emphasize the importance of fertility, with prominent phallic figures and wide-hipped female figures making up the majority of early art in areas such as Denmark.
Most scholars draw parallels between these figures and Freyja and Freyr, gods of earthly fertility.
What Is the Main Source of Norse Mythology?
The primary sources of Norse mythology are the Eddas. The Eddas consists of a collection of poems (author unknown) and a prose retelling of selected Norse mythological tales written by Snorri Sturluson.
This 13th-century account of Norse mythology is a later recollection of tales reflecting Christian changes.
The Eddas are the ultimate source of Norse mythology that still survive, even if they are brief and embellished accounts of the traditional tales and beliefs of the Scandinavians. 
However, there are several other medieval sources for Norse mythology, which include:
- The Gesta Danorum, Acts of the Danes, by Saxo-Grammaticus, 12th century AD
- Heimskringla, History of the Kings of Norway, by Snorri Sturluson, 13th Century AD
- Historia ecclesiastica gentis Anglorum, the Ecclesiastical History of the Angles, by Bede, 8th century AD
- The Íslendingabók, Book of Icelanders, by Ari Thorgilsson, 12th century
- The Landnamabok, Book of Settlements, by Anonymous, 12th century
Thus, when creating a timeline of the literary evidence regarding Norse mythology, there’s one biased account of Germanic religion from the 1st century and a vast gap lasting until the 8th century.
Then, in the 11th and 12th centuries, writers seem to take a new interest in chronicling the history and religious practices of the Scandinavians — likely due to higher literacy rates and the influence of Christianity.
Norse Religion vs. Germanic Religion
While Norse and Germanic religions and mythologies have much in common, minor differences exist.
Most notably, the main three gods in each religious system differ. In Norse mythology, Odin, Thor, and Freyr are the most frequently worshiped, while in Germanic Mythology, Wodin (Odin), Donar (Thor), and Tyr are the most important gods.
Likewise, the naming of these gods differs, as seen in the example above.
Germanic mythology does not usually include the Vanir, a group of gods associated with earthly fertility. These gods, which included Freyja and Freyr, were very popular, especially in rural areas in Scandinavia.
Much of the earliest evidence for the Norse religion stems from these deities’ wooden and metal idols.
The focused worship of the Vanir is a testament to another difference between these belief systems. Norse religion was much more focused on fertility, agricultural production, and trade than the Germanic religion.
On the other hand, the Germanic religion placed a greater emphasis on war. That association is likely due to the many wars the Germans faced before and during the Roman conquest.