The vast majority of what is now known about Norse mythology, however, survives thanks to Snorri Sturluson, an ambitious and powerful chieftain, lawyer, politician, poet, and saga writer who lived in Iceland from 1179 to 1241. These dates are significant: They tell us that Snorri was recording these narratives roughly 200 years after the Christian conversion in Norway, Denmark, and Iceland. They also, significantly, tell us that “original” and definitively pagan narratives about the Norse pantheon do not actually exist.

This claim needs a bit of qualifying. Scholars mostly agree that the myths Gaiman has retold—the same ones found in Snorri’s Prose Edda—were inspired by earlier pagan narratives. In fact, several stanzas of pre-Christian poems are preserved in Snorri’s work. Other snippets of pagan poetry also appear in 13th and 14th century Icelandic sagas, truly novelistic accounts like Grettis saga and Egils saga (the latter also possibly written by Snorri). Yet by the time Snorri was composing his versions of the Norse myths, his worldview was solidly a Christian one.

Even if, for the sake of argument, it’s accepted that Snorri was channeling his pagan ancestors at the time of writing, that they were completely accurate 13th-century reports on pre-Christian mythology, we’d still be none the wiser for doing so. The versions of the Norse myths Snorri heard and recorded aren’t necessarily the same ones being read and circulated today. At least, not precisely. Most scholars agree that Snorri’s Prose Edda was completed around 1220, but the three primary manuscripts containing these stories that are still available to us today date between the 13th and mid-14th centuries. At some point over the course of 130 years, Snorri’s myths were collected along with various other early medieval works, and included in compilations that are sometimes abbreviated, often incomplete. It’s possible that one of these manuscripts is a direct copy of Snorri’s text—but even so, it is still a copy. Overall, there are gaps in these narratives. Missing pages. Lines of text packed densely onto vellum (in places, almost illegibly) to save precious space. These manuscripts capture the hands of different scribes at different moments. They are projections into the past reflecting Snorri’s own rearview projections. It’s impossible to say what shape the myths may have taken before these transcriptions, much less before Snorri himself wrote them down; we cannot make arguments out of silence.

Readers hoping for a fully novelistic reinvention of these myths in Norse Mythology will be disappointed. Gaiman has neither fabricated passages that might fill lacunae in existing manuscripts, nor concocted new adventures for old gods. Instead, Norse Mythology is a considered retelling of sixteen familiar tales, presented in virtually the same sequence as they are found in Snorri’s Prose Edda, and crafted as sympathetically as any modern author can. There are echoes of Ibn Fadlan’s account, for instance, in Gaiman’s description of the funeral of Odin’s second son, Balder, one of the most beautiful and beloved of the gods. Like the noble Rūs man whose body was brought to the riverside, laid in a ship there, and burned with a woman by his side, Gaiman’s Balder was brought down the shingle, and when his wife “saw her husband’s body carried past … her heart gave out in her breast, and she fell dead on to the shore. They carried her to the funeral pyre, and they placed her body beside Balder’s.”