Sources for the reconstruction of pre-Christian traditions include the accounts of the Anglo-Saxon missionaries to the region, medieval and modern folklore and legend, and local toponymy.
The first epic heroes, kings and leaders of The Low Countries, considered mythological, in the sense of supernatural and foundational, include: Objects considered magical or sacred in the Low Countries (7th century) included: Oak trees, springs and wooded groves had sacred and medicinal powers.
After the influence of Christian missionaries, the original mythologies were lessened in power, and for the most part adapted into folklore and legends, often made diminutive.
In the Hieronymous Bosch painting, Cure of Folly, 1475-1480, the woman balancing a book on her head is thought to be a satire of the people wearing phylacteries.
The vita of Willibrord records he went on a missionary journey to an island called Fositesland (most think this was Helgoland occupied by ethnic Frisians), between Friesland and Denmark.
Willibrord found it had sanctuaries and shrines dedicated to the Scandinavian gods Fosite, son of Balder and Nanna.
Willibrord took other mission trips on the Dutch mainland where he witnessed that the people considered clearings in woods, springs and wells sacred to their mythology and religion.
When he arrived, Bonifatius found that the Frisians had restored and rebuilt their fana delubrorum, the heathen temples, after Willibrord had been driven out.
Bonifatius joined Willibrord in Utrecht to receive a three-year missionary training, then in 721 travelled east of the Netherlands into Hesse, Germany.
Bonifatius undertook a final preaching mission in Friesland in June 753 when he was attacked and killed by a group of Frisians with unknown (legend says resentful) intentions.
... [Do not] make vetulas [a type of corn dolly], little deer or iotticos or set tables [for the house-elf] at night or exchange New Year gifts or supply superfluous drinks [a Yule midsummer custom]...No Christian.
No Christian should presume to invoke the name of a demon, not Neptune or Orcus or Diana or Minerva or Geniscus... No one should observe Jove's day in idleness.
... No Christian should make or render any devotion to the gods of the trivium, where three roads meet, to the fanes or the rocks, or springs or groves or corners.
"[10]Procopius in the 540s records a belief and/or funerary rite observed at the mouths of the Rhine involving the passage of the dead to the island of Brittia (Great Britain).
Among them, the story of The Legend of the Wooden Shoe, clearly begins with fragments of Druidic mythology in the ancient Netherlands retold for children: "In years long gone, too many for the almanac to tell of, or for clocks and watches to measure, millions of good fairies came down from the sun and went into the earth.
Many regional legends exist in the Low Countries about the origins of natural landmarks such as hills, bodies of water, springs, wells, forests and the sea, that attribute creation to the ancient gods.
Other legends tell where different witte wieven lived on as spirits in the Middle Ages, which are probably recharacterized stories of sacred sites.
Many nice examples were collected in the book Veluwsche Sagen by Gustaaf van de Wall Perné (1877-1911).
The Veluwsche Sagen was a historically researched collection of Dutch "sagas" from the legends and folk almanacs in the province of Gelderland: The creation of the Uddeler- and Bleeke Lake(s): This myth concerns a battle that allegedly took place between Donar the God of Thunder with the winter giants and the "Midgaardslang" (a giant snake monster) who strategically align against him.
Donar attacks, riding through the air on "his billy-goat wagon", the sky blazes and the earth trembles because of his "never missing thunderhammer."
Then the earth sank into the sea, the seagod blew a horn and a big black ship came to collect Donar's body.
The grave of Midgaardslang became overgrown with the forest nearby, until in 1222 a bright flame shot out of the pool and the ghost of the snake wriggled up and fled north.
[13] An ancient stone altar dating from around the 2nd century CE found at Cologne (Köln), Germany is dedicated to the goddess Vagdavercustis.
[16] In the now flooded sites of Domburg and Colijnsplaat, on the East Scheldte Estuary, there are the remains of temples each dedicated to a deity Nehalennia.
According to the tradition (The Legend of the Wooden Shoe), the trees were filled with good spirits, and kept the land firm otherwise it would melt or disappear under water and floods.