Something on the historiography

There's never really any consensus on these kinds of things; until the 20th century there was a strong tendency to put great stock in the sagas and chronicles like Gesta Danorum, Chronicon Lehtrense and Historia Norwegie. But as I mentioned in a short overview of historiography (in re: Vinland), there's always been those who've been skepical, like the swede Olaus Petri. Petri was most famous for championing the Protestant Reformation in Sweden. In the 1530s he wrote a history of Sweden where he made clear that he considered these sources to essentially be a load of unreliable rubbish. The Swedish chronicles say the Danes were defeated countless times and the Danish ones say the Swedes were humiliated just as much.. who knows or cares? Although this source-critical attitude and attempt at being even-handed is commendable in today's POV, in his own time it meant nobody saw any point in reading or publishing such a history. It was not printed until the 19th century. (IMHO, it remains an under-examined word to this day too considering we know he had access to some medieval sources that are now lost)

Academic interest in mainland Scandinavia for the Icelandic literature began in the 17th century. From then up until the start of the 20th century, they were by-and-large taken at face value by most historians. The obviously-fantastical elements were disregarded or reinterpreted as a mythologization of some actual event. Sometimes it seems as if they were prepared to seriously discuss almost any proposed theory on the origins of particular stories except the possibility that they'd simply been made up. The older poetry tended to be assumed to be much older than we now believe it to be. For instance, Völuspá was considered to be perhaps as old as the Roman Iron Age, while today it's considered Viking Age, perhaps even Late Viking Age. Which has significant ramifications, as you can't discount the possible (or in today's view probable) influence of Christian eschatology on it.

So as I'd said, as late as the 1920s or 1930s it's not that uncommon to find papers by big-name historians that, for instance, assume the historicity of the Yngling kings, whereas today that would be a pretty fringe position.

Lauritz Weibull is the name I usually drop if I had to name just one who brought about higher level of source-criticism in studies here.

Weibull took the sagas to task; for instance he completely trashed Jomsvikinga Saga. He pointed out that the Jomsvikings were never mentioned in contemporary sources. They turned up several centuries after they'd supposedly existed, and the exploits attributed to them had previously been attributed to others. Their "Jomsborg" (the castle, not the actual town Jom/Wolin, which did exist) did not resemble any castle that'd ever existed in that period. Although there's no doubt some vikings lived in Wolin and even more visited it, the legend of the Jomsvikings was on the whole a later, medieval construct.

This was not just a debunking of that particular saga but a case study on how these legends proliferated and grew over time. Therefore, contemporaneity was the big lodestar here.

So for most of the past century, the early (Scandinavian-) medieval chronicles and Icelandic fornaldarsögur have been considered highly dubious sources. Although things have moderated somewhat, I don't think there' much disputing this revisionism was a well-needed "spring cleaning" of all the far-fetched ideas and theories that'd proliferated up to that point.

It wasn't an entire clean sweep though; pop-cultural notions lived on, as did the generalizations about the notion of a homogeneous "Norse" culture and religion, which've come under quite a lot of challenges in recent decades. I could (and frequently do) go on all day about that stuff but to get back to written sources..

Prose vs poetry

The most primary of written sources we have are runic inscriptions, out of which the great majority of preserved ones from the viking age or earlier are on stone. The vast majority of those are 11th century stones that are highly formulaic, along the lines of "[Person 1] raised this stone in memory of [Person 2], his/her [relation]. [Person 3] carved". Even the longest inscription (the Rök stone) is only 760 characters. So there there's very little information here from the content of the texts. A statistic over (for instance) the number of carvings commissioned by women says more about the society than most inscriptions do.

But we do have stuff from the Viking Age in the texts written down later in the 11th and 12th centuries; and that's the skaldic poetry. Which is not to say that all poetry is old; on the contrary, the main motivation of Snorri Sturluson in writing his Edda was to promote the composition of traditional poetry.

As said, the older poetry is not nearly as old as some once believed, but some of it does date from the Viking Age and is likely more or less verbatim although not necessarily complete. The dating is primarily because the language itself is more old-fashioned than when it was written down, and the believed cause for this is that it's more difficult to change words in poetry without screwing up the meter and alliteration. (Norse poetry is not rhyming but alliterative) The prime source of this poetry is the Elder (or Poetic) Edda, but there are also some quotes of it in Snorri's Edda and other manuscripts.

There is little in the poetry which 'depicts the viking age' though; they're typically about gods and legendary figures; some derive from transferred European legends about historical figures. For instance, Attila the Hun became the source of Atli in Atlakviða, whereas the Gothic king Theoderic became Þiðrek from Bern. So most of what we have that could actually be dated to Viking Age Scandinavia does not take place there or then. Some which is "based on" historic figures have little but the name left in common. The poetry is also often quite opaque, first just by being poetry but also since Norse cultures were quite fond of riddles, allusions and inventing arcane synonyms and by-names.

But what we can say is that some of these stories really were well-known these times; The picture stone Ardre VIII from Gotland depicts for instance the story of Völund (Wayland) the smith. It has enough details in common with the saga account (written down 400 years later) for there to be a consensus on that interpretation. But it is one of few such picture stones where there exists that kind of consensus on their interpretation.

In Snorri Sturluson's Edda, he elaborated a bit on some of this poetry and at least to some extent he must have been relating old folk stories. An example of this is that in his elaboration on the story of Thor's Fishing (which exists in art as far back as the 10th century) he mentions Thor's foot going through the bottom of the boat. This detail not known from any other written source is also present on the Altuna runestone from the mid 11th century. Runestones also have the occasional quote or turn of phrase that is echoed in the poetry. (e.g. there are two rune stones that describe runes as being reginkunnum - originating from the gods - the same way they are in the poem Hávamál)

Snorri criticism

Snorri is the single most important source, both on mythology (through this Edda) and history (through Heimskringla). Traditionally much of Snorri's writings were taken at face value as true.* Pop-books on Norse mythology tend to always do so, but even in academic research there are many who perhaps trust him more than they should. There's always been a concern that Snorri (as a Christian) may have introduced Christian elements, such as creating a light-and dark-elf distinction not otherwise attested to mirror Christian concepts. Or that he may have modified the Baldr story which we have an earlier and dramatically different account of in Saxo Grammaticus' version, and which seems to have stronger Christian and Greek mythological parallels. But more recently the question's also been raised of how much of Snorri's expanding on the poetry is simply his own - and not always correct - interpretations. For instance, Rudolf Simik argued that the division of the gods into two groups (Æsir and Vanir) may have not even existed, but vanir had simply been an archaic word for 'gods' that Snorri misinterpreted as a proper noun and thereby invented a separate group of gods. Which seems a shockingly plausible revision given the amount of ink spilled over researching these perhaps-chimeric groups of gods.

So is Snorri reliable or not? It's probably not the case that Snorri was intentionally trying to distort the past. But the version of it he wrote was largely his own, particularly his euhemerism, the explanation of the origin of the pagan gods as historical human kings. That said, it should still be reiterated that Snorri did in fact write down some authentic traditions we don't know from anywhere else. But historians today do not take him at face value to the extent they once did, nor to the extent pop books on Norse mythology usually do.

There is not a clear-cut boundary line, regrettably. There used to be, to be sure; the 14th-century "Postclassical" sagas were thought of as artistically and historically inferior by pretty much every major scholar in the field in the 19th and the first half of the 20th centuries. But these have been the subject of ever-increasing amounts of scholarly attention in the past 50 years, which has, in my opinion, fairly thoroughly dismantled that line.

Because the saga sources are derived from (but are not a slavish transcription of) oral traditions, they always operate in a blend of genuine historical information and later interpretations of what life must have been like. The interpretations are filled in by contemporary social concerns, other textual sources, etc. Therefore, a saga like Yngvars saga viðförla, which may tell of an expedition to the Rus that we have runestone evidence for, still draws on the Liber Monstrorum and, indirectly, Isidore of Seville's Eymologiae.

Another example could be Njals saga. The legal evidence there has been persuasively argued to match with Gragas, a law code that was no longer in use at the time the saga was composed; therefore, there seems to be some amount of genuine reflection of laws going back to the Viking Age. However, the environmental information depicts a kind of "golden age" of prosperity for Iceland that never existed to the extent that it is described. And, the account of the establishment of the 5th court in Iceland actively contradicts the story given by Islendingabok, the early 12th century history of Iceland.

A third example here would be Hromundar saga Gripssonar, which we only have in a version derived from poems derived from the older version. However, according to the 13th century Þorgils saga ok hafliða, this saga was told at a wedding in 1119. So far, so good; it's old, and so maybe is a more genuine reflection, in some ways, of the Viking Age. But, we run into problems in the same chapter; Hromundar saga was called a lygisaga "Lying saga" by King Sverrir of Norway. This seems to very clearly indicate that this old saga was not regarded as an actual depiction of the Viking Age or of Hromundr's life by the mid-1200s at the latest.

In my opinion, I strongly hesitate to use any saga source, no matter how old, as a "genuine" reflection of the Viking Age. Certainly, there are genuinely old elements in even very young sagas, and plenty of ink has been spilled trying to separate the old elements (an undeniably worthwhile endeavor); however, treating them as reliable I think misunderstands why the sagas were created. With exceptions, the sagas seem to present a history as the author/scribe wanted it to be, which is a far cry from modern history. They certainly are presenting themselves as historical, and sometimes acknowledge when they make a choice about which of two version are more reliable, but they are much more revealing about how people thought about their past than they are about that past themselves. Each version of a saga is a different commentary on the past, and treating them as such has proven very fruitful in saga studies over the past 20 years.

So, long answer short; there is no cutoff or consensus anymore, every saga blends elements across the Middle Ages to varying degrees, but trying to determine which ones are "factual" depictions of the Viking Age obscures a lot more interesting questions and historical information in the sagas.

Thank you for taking the time to give such well explained and thorough answers. Very interesting read on a very thought-provoking matter.