This is an extract from an article called KNOTS OF DEATH by Alby Stone,
which appears in WEB OF WYRD #7.

A number of Viking monuments feature a curious design known as
the valknut, the "knot of the slain" or, more loosely, "the
knot of death". On an 8th century CE picture stone from
Hammers in Larbro, Gotland, it consists of three interlocking
triangles. This stone, now in Stockholm's National
Historical Museum, is divided into several panels; one of the
central panels, in which the valknut occurs, depicts several
motifs that suggest some sort of connection with the cult of
Odin - an eagle, a flying figure - possibly a valkyrie -
holding a ring, a man being hanged from a tree and a group of
three warriors - with shields and upraised swords - led by a
fourth man who seems to be holding a large bird of some kind.
The valknut is adjacent to the eagle and below it are two men,
one with a spear, who appear to be engaged in placing a corpse
inside what looks like a burial mound. Between them and the
hanged man is what appears to be another, smaller, valknut of
the same design. This type can also be seen on a rather
splendid golden ring discovered near Peterborough, Cambs, and
currently on display at the British Museum in a cabinet
labelled as containing Anglo-Saxon "secular" metalwork.
Another picture stone from Gotland (Tangelgarda also in
Larbro) has a panel showing a rider being welcomed by a woman
holding a drinking horn with four men who are holding rings.
The woman may be a valkyrie, a "chooser of the slain", one of
whose functions was to serve ale to the Warriors in Valhalla,
another pointer to the cult of Odin. The rider has a valknut
behind his head and there are two more among his horse's legs.
On this stone, which can also be seen at the Swedish Museum,
the valknut is made up of a single line, interlaced to make
three triangles.

A fourth type of valknut, rather different from those
described so far, occurs on a stone cross from Andreas on the
Isle of Man and is now in the Manx Museum, Douglas.
This version is basically a simple knot "tied" in such a way
as to retain the basic tripartite structure of the versions
mentioned above. Unlike the others it is not a closed
structure but its identity as a valknut, while mildly
contentious, is not really in doubt. The scene in which it
appears shows a man, evidently Odin, holding a spear pointing
downward as he is devoured by a great wolf. An eagle perches
on the man's shoulder and the valknut is at his side. The same
design appears elsewhere, on a stone discovered in 1822 at
Gosforth and now incorporated into the structure of the local
church. It is between the back legs of a horse. On a picture
stone from Alskog, in Gotland, it occurs twice among the eight
legs of Odin's horse, Sleipnir. Despite this seeming wealth of
examples and the diversity of styles the valknut itself has
remained enigmatic. It seems to be associated with horses,
particularly with the steed of Odin, and the cult of Odin in
general. Motifs associated with the symbol include the hanged
man, valkyries, bears, and the scene from Ragnarok on the Manx
Cross, all indicating some connection with Odin. According to
HR Ellis Davidson, the valknut also appears on the funeral
ship excavated at Oseberg, Norway in 1904, and on the tapestry
found in that vessel, indicating some sort of funerary
association.

The origin and meaning of the symbol are extremely difficult
to discern, as is its association with Odin. Obviously it has
a decorative value as distinct from its symbolic meaning. The
valknut has been used as a motif by Scandinavian weavers since
the Viking Age. Indeed, it is recognised as a traditional
design in that part of the world quite apart from its alleged
occurrence on the Oseberg tapestry. Davidson opines that it is
related to the Celtic triskele, the three-legged symbol most
familiar as the emblem of the Isle of Man and linked with the
Irish God of the sea, Manannan. The triskele is essentially a
variety of the swastika, a common enough cosmological symbol,
but neither can be said to possess the characteristic
interweaving of the valknut. While it may be unwise to dismiss
a possible relationship between triskele and valknut, it must
be said that any resemblance is purely superficial, lying
solely in their tripartite structures. Structurally the
valknut has more in common with the Celtic triple spiral motif
which is also found on Old English and Pictish artifacts and
much older objects. Unfortunately there is a dearth of hard
evidence for the mythological or religious significance of the
triple spiral, which tends to occur within wholly abstract or
symbolic designs, but it occurs within funerary contexts and
has been linked with the female principle by various scholars.
The various types of valknut, their contexts aside, share two
important characteristics: they are tripartite and they are
constructed by interweaving or interlinking.

In Old English texts the term "wyrd" is, despite its other
connotations, frequently used to denote death rather than a
structured and unfolding future that is suggested by the
functions of the Nornir and their Greek and Roman
counterparts. There is of course an intimate relationship
between the two concepts and death is after all the fate of
every being. Scandinavian myth makes it clear that there are
only two things which the gods cannot avert; fate and death.
In Norse myth the name of the senior Norn is Urdr, a word in
Old Icelandic that can also denote a burial mound or cairn.
"Beowulf" and other texts characterise wyrd as a weaving of
webs but the word usually means nothing less than the moment
of death, or at least the events leading up to death.

The "Beowulf" motif is revealing, however; it has already been
noted that the fates tend to be spinners or weavers and in
this instance there is also the idea of a snare, which can
refer back to the Indo-European goddess of death as described
by Lincoln. Like Hel, the Nornir reside in the far north, at
or near the celestial axis and like her they reside "below
ground", where the World Tree has its roots. The Nornir
determine life, span and the time of death, while Hel takes
the dead to her cold bosom. All these characteristics are
shared to some extent with Odin, as is their femininity,
apparently adopted by Odin in order to engage in seidr - the
natural magic of womankind.

At the very least, Hel and the Nornir are closely related,
perhaps even deriving from the same proto Indo-European
goddess, and Odin has acquired some of their characteristics
by virtue of his association with the cosmic centre, the
structure of which reflects their own nature. If the valknut
symbolises anything then, it is probably either wyrd, death,
or perhaps even the Nornir themselves, who are more or less
the same as wyrd anyway. Exactly when the valknut would have
come to represent these is difficult to estimate. Certainly
the examples here all date from the Viking Age and appear to
range in time from about the 7th to the 10th centuries CE. I
am not aware of any valknuts of a significantly earlier date.
It is interesting that in England the use of the valknut seems
to have died out with the establishment of Christianity and
the consequent decline of heathenism. The Nornir are not
represented pictorially anywhere in the Germanic world, which
is rather surprising. A panel of the Franks Casket shows three
hooded figures who might be intended as a likeness of that
fateful trinity, but it is by no means certain. Until any
conclusive artifacts come to light the truth of the matter
must remain as uncertain as the workings of the Fates
themselves.