• Hans Faber

Groove is in the Hearth

The hearth was in pre- and early-medieval times the holy of holies, the heart of the family. Where you would lay back and groove. Groove on the sound of the endless rains on the thatched roof. Or, the sound of the sea water at your feet below. Sloshing against the grassy slopes of your house platform. A place that was warm and soulful. Filled with good spirits and minds. But how did those early Frisians manage to keep the evil spirits, creatures and sickness at bay? How did they protect their yards and houses from this darkness? Well, dig this. They did it with grooves.

In this post we focus on the terp region (a terp being an artificial settlement platform). The terp culture existed in the west of Flanders, the north of the Netherlands, the northeast of Germany, and the southwest of Denmark. This saltmarsh culture is as old as 2,600 years, when the first mounds were raised. After the Romans arrived at the beginning of the common era, we learn the names of the coastal dwellers. It was the territory of the Frisii or Fresones ‘Frisians’ in the west, and the Chauci in the east.

Where exactly the border between the two tribes ran, cannot be determined anymore. According to the second-century Greek scholar Ptolemaeus, the River Ems was the border between the Phrissioi ‘Frisians’ and the Kauchoi ‘Chauci’. However, archaelogical research shows closer kinship of the province Groningen with the Chauci in the east, than with the Frisians in the west (Nieuwhof 2021). Today, this river is a border still. Now between Germany and the Netherlands, although the exact course of the border in the Dollart Bay is disputed between the two countries to date.

After the Roman Period and the Migration Age, the whole area between Sincfala, i.e. inlet the Zwin in Flanders, and the River Weser had turned into the territory of the (new) Frisians. Also, much of the Wadden Sea coast of Schleswig-Holstein was colonized by Frisians from the Ealy Middle Ages onward. The region known today as Nordfriesland. Region Nordfriesland was not part of political Frisia between Sincfala and the River Weser. From the High Middle Ages West Frisia was under control of counts of Flanders and of Holland. Frisia still encompassed the area between the Vlie and the River Weser, in other words the current provinces Friesland and Groningen, and region Ostfriesland. This more or less would continue to be the status quo until the sixteenth century, when the remainder of Frisia was dissolved too.

1. Early Frisians, oracle rods, and all that

The second-century Roman historian Tacitus wrote about the religious, pagan practices of the Germanic tribes in general. For example, that the people did not depict their idols as humans, and that they worshiped their gods in open-air somewhere at a lo, an open spot in a forest (Van Renswoude 2021). Women could be fortune-tellers and could possess the gift of prophecy. Casting lots and human sacrifice was also part of Germanic rituals. White horses, living 'freely' in the woods, could warn people, and could predict future events. There is very limited information about the gods the Frisians worshiped, both the Frisii and the Frisiavones. Several names of idols and matres we do know, but basically here our knowledge ends.

Almost two hundred so-called oracle rods, being used to cast lots with, have been recovered, especially in the region northwest Germany and in the Netherlands. These are dated from the Roman Period into the Middle Ages. Even the practice of casting lots was incorperated into the late eighth century Lex Frisionum. The Lex Frisionum was the codification of the laws of the Frisians ordered by the christian, Frankish kingdom. Therefore, the practice of casting lots was modified as being a sign of God to determine who was guilty when in a riot someone was killed (Hines 2021). And, are we not still talking about 'it is someone's destiny' and do we not all love the lottery? Casting lots, therefore, is a pagan practice that survived christianization. The oracle rods were made of silver, bronze, bone or horn. According to the same Tacitus, these were made of branches of fruit-bearing trees. It might these wooden lots did not survive the passage of time, of course.

Not only mankind was submitted to lot or destiny. Interestingly, the gods too. This make you wonder, what was lot? Maybe it were the Fates of Greek mythology. The Fates, a trio of goddesses, determined the destiny of each humans. One of the three goddesses was Clotho. It made wool and spun the Thread of Life. Goddess Lachesis measured the lenght of the thread, and goddess Atropos cut the thread with its shears. Wool production was a major and crucial economic activity for the coastal Frisians, and it handicraft was protected by the Lex Frisionum. If you would hurt a spinner, you had to face very severe punishment. Again, was lot was spinster of wool, again a woman giving calling the shots, or, indeed, pulling the strings.

In European folklore, spinning and weaving wool was linked to the world of fairies and myths. Scottish weavers offered milk to the Highland fairy named Loireag. Then there is the Germanic winter spirit called Berchta, also known as Perchta, Frau Holle, and Mother Hulda. In this tale, the stephdaughter is pricked by a spinning wheel, which sets the events in motion. Also Sleeping Beauty, or Toarnroaske or Doornroosje, is pricked by a spinning wheel. In Wales exists the fairy spinner Gwarwyn-a-Throt, and in Ireland the fairy spinner Girle Guairle. Furthermore, in medieval Scandinavia a female spirit called seidr existed, meaning thread. Read our posts Haute couture from the salt marshes and Recuing rolling sheep to get a bigger picture of the importance of wool.

But, what were the gods of the early Frisians?

Firstly, the goddess Baduhenna. Known from the Battle at the Baduhenna in AD 24. A battle just north of the modern city of Amsterdam between the Frisii Minores 'lesser Frisians' and the Roman Army, with on Roman side a body-count of 1,300 soldiers, according Tacitus.

Secondly, the goddess Hludana. Known from an inscription found in Xanten at the lower River Rhine in Germany. But also from an inscription found at Beetgum in province Friesland. Perhaps Hludana was worshiped by the Frisii Maiores 'greater Frisians', living in the northwest of the Netherlands.

inscription Hludana, Beetgum Frisia
stone Beetgum

The inscription reads: "To the goddess Hludana, the fishing contractors, when Quintus Valerius Secundus acted as tenant, fulfilled their vow willingly and deservedly."

Thirdly, the matres Frisiavae. Known from an altar stone found in the town of Wissen halfway between Cologne and Frankfurt. How it ended all the way up there, we have not got the foggiest idea.

Fourthly, the goddess Nehalennia. Known from the hundreds of stone-altar parts found in the waters near the settlements of Domburg and Colijnsplaat, both in province Zeeland in the southwest of the Netherlands. This used to be the territory of the Frisiavones, the so-called Romanized Frisians (IJssennagger 2017). Not only Frisians, but skippers and traders traveling to Britannia from Trier, Cologne, Nijmegen etc, made offerings to Nehalennia for a safe passage sailing the Channel at Domburg and Colijnsplaat too. Read also our post Island the Walcheren: once Sodom and Gomorrah of the North Sea to find out more about Nehalennia.

Lastly, fifthly, we present you the gods worshiped by the Frisians known from votive inscriptions found all the way in northern Britain. These gods were not worshiped by your average Frisian. They were mercenaries in the Roman Army fighting in Britannia, and who were deployed at Hadrian’s Wall. The goddesses they worshiped were the two Alaisiagae, named Baudihillia and Friagabis. Read our post Frisian mercenaries in the Roman Army to read more in depth about these soldiers of fortune. Casually, these mercenaries also erected a pillar dedicated to the god of the thing. The thing being the Germanic assembly, also known as ting, ding or þing. Check our post The Thing is... to learn more about these soldiers with a democratic nature.

Of all the gods mentioned above, we do not suggest these were specific Frisian gods. We merely explained these were Germanic-Celtic gods worshiped (too) by the Frisians. And not even that conclusion is definitive. The picture of these ‘Frisian’ gods is that it were deities, goddesses, women. This fits nicely with what we know from other native Germanic-Celtic gods during the Roman Period, namely that they were all feminine too. It is also consistent with what Tacitus wrote about the specific powers attributed to women, mentioned above.

mask of Boerdam Middelstum Frisia
mask of Boerdam, near Middelstum, ca 500 BC

On some of these rituals we know that they were still practiced by the (new) Frisians in the Early Middle Ages. It was the seventh-century Saint Wulfram of Fontenelle, Archbishop of Sens, who pleaded with king Radbod of Frisia not to perform human sacrifices. A king described as the Enemy of Christ and as homo omni fera crudelior et omni lapide durior meaning: a human being more savage than any wild beast and harder than any stone. The killing could be executed by either hanging, or by tying someone up at a pole in the sea during ebb tide to let him or her drown slowly, after being castrated among other.

The latter practice is also documented in the already mentioned Lex Frisionum, where tying up someone to a pole to be drowned by the rising sea, was a punishment for sacrilege of temples, and therefore not a sacrifice per se but also a punishment. By the way, Saint Wulfram is also known from the famous failed baptism of king Radbod. For this piece of history read our post Finally, king Redbad made his point in the European Commission – via Facebook. And, as explained above, the pagan practice of casting lots survived christianization as well and was still practiced in the Middle Ages.

By the way. The image above of the Boerdam mask, is easily associated with pagan rituals. However, when a school class asked the professor why it was not just made for fun, he not really had any arguments against it (Nijdam 2021).

mask of Boerdam by Kelvin Wilson

2. How about those grooves?

Not any different from today, for terp dwellers too, it was important that their land, farmyards and houses were free from evil spirits and souls, and from infectious deceases and sickness. The concept they used might have been a barrier model. Similar as the innovative models still being used by policy makers on security, defense and migration. Or, like the force fields in '80s science fiction movies or video games. The old Frisians too drew imaginary circles, with the hearth of the house annex farmstead being the center.

It fits very well with the physical, radial lay-out of a terp village. An artificial, circular mound on flat and treeless tidal marshlands. The, first, outer ring were the salt marshes bordering the sea. The surrounding land starts with mud, and toward the terp settlement it slowly becomes more solid and suitable for cattle to graze and even crops to grow. Often, the more inland marshlands were protected with low so-called summer dikes, which offered protection against regular, daily flooding. Spring tides and storm floods still inundated the marshlands, think of ten to twenty times a year.

Knudtswarft 'Knudt's terp' at Hallig Gröde, Nordfriesland by Wilhelm Dreesen (1895)

The next, second ring were the flanks or slopes of the terp itself, which were used for cultivating crowing crops, cutting sods for construction, and for crafts like weaving, blacksmith, pottery and alike. The inner circle or third ring, was the terp village with houses and sweet water well(s). The well itself contained often deposits as well, like spoke wheels, horse heads etc. Probably also with a ritual meaning. An interesting artifact has been found in a dung pit in the terp of village Wartena in province Friesland, namely a wooden phallus. It is dated the Roman Period.

When it comes to ward off evil spirits, souls, sicknesses and death, the hearth was the center. The hearth itself was protected too, testifying frequent deposits found underneath it. Sometimes pieces of wooden wheels were excavated. If interested why wheels were buried and sacred, read our post Celtic-Frisian heritage: there’s no dealing with the Wheel of Fortune. Remember, do not mess with wheels!

Now, from the already radiant patron of the salt-marsh landscape, let's turn to the circular barrier model of defense. We go through the force fields from the inside out.

first line of defense

The first ring was the house, its walls and its doors. Underneath the poles supporting the roof and/or the doorframe, deposits were placed. These could be, for example, animal bones, terra sigillata and small pots with, perhaps, food offerings placed in it. Other deposits found during excavations of terps, are locks of hair. These locks might also have been part of rites of passage, for example a boy turning into a man or warrior, or a girl turning into a woman, and therefore not part of the energy giving rituals for the force field. Also, often at the base of the walls of the houses, skulls of cows, horses and dogs were placed (see image below).

excavation Ezinge
home wall protected with bones, excavations terp Ezinge, province Groningen - Iron Age

second line of defense

The second imaginary circle was created immediately around the house. Indeed, this was done by digging grooves, or furrows. Besides, these ditches probably functioned as little channels to collect rainwater falling from the roof into the groove and transporting it to the central sweet-water wells, these grooves also functioned as protection against evil spirits. Collecting rain water was vital for the terp dwellers, since sweet water was often scarce at the salt marshes. The Roman Pliny the Elder wrote already in the first century about these water pits, read our post Shipwrecked people of the salt marshes.

third line of defense

Then, the third circle. This was the farmyard itself. The force field of the yard was energized with all kinds of deposits, mainly placed in pits. It could be clay pots, again with possible food offerings inside, animal bones and potsherds. Complete skeletons of horses and, regularly, of big dogs have been found too. For more about this fearsome war dogs, read our post How to bury your mother-in-law.

fourth line of defense

The final, fourth, circle was made by another round of grooves, furrows and ditches. These bordered the yard. Again, in the ditches deposits were placed. This could be in-tact (miniature) pots, pottery, potsherds and animal bones. Not always, but pots and pottery also were smashed when deposited. Sometimes even bronze Roman statuettes and brooches were placed in grooves. If the ditches were filled, e.g. because of a terp enlargement, again ritual deposits were being made. Why disband a good protective force field, after it was sealed off? Or, was it a way to say ‘thanks’ for all the protective work done the years before? Some archaeologists argue that deposits were being made when a groove or ditch was dug in new land as a means of compensation for the goddesses and spirits for the infringement of ‘their’ lands (Tuin 2015).

deposits in water by S.J. Goetze

But not only bones and skulls of animals were used…

Excavations in the terp region identified human bones and skulls literally lying all over the place. These bones were used to strengthen the protective power of the circle. Albeit the dead normally were not buried in the terp mound itself, and excarnation above ground was the common funeral practice during the Roman Period (Nieuwhof 2015), occasionally complete inhumations, both adults and infants, were found under the floor of the house or on the yard. Mostly within a radius of ten to twenty meters. Mandible, femur, tibia, vertebra and skull fragments, all have been found in pits, grooves and ditches. Do not be too alarmed, ritual use of human bone is comparable with the relics of Catholic saints of today. These relics still serve as an intermediary between heaven and earth (Van Eijnatten & Van Lieburg 2006), and as a protection against evil and sickness.

Human skull-bone was even worked. Polished, and a hole was perforated into it so it could be used as an amulet. These human amulets and cups have been found in the terps of Arum-Baarderburen, Marrum-De Beer, Stiens-Kramer, Hempens-Glins, Ezinge and of Wierhuizen. Your deceased mother or grandma always close around your neck, and making it difficult for you to breath freely still. The worked skull pieces might even have been used as cups. Or, another possibility, were it former enemies hanging around their necks? And if you think all this is just too weird again, think of the millions of people who perform the holy rite of the Eucharist today, and who then consume the blood and flesh of Christ.

Also, read our post How to bury your mother-in-law to learn more about the pagan excarnation practices at the salt marshes, including the role the big Frisian hounds of hell had in releasing the soul from the flesh.

cups and amulets made of polished human skull, terp region Frisia - Iron Age / Roman Period

Many of the practices above date from the Roman Period, the Iron Age. But some of the rites and rituals probably survived well into the Early Middle Ages. By then, the Frisians had become your average, classic Germanic tribe. No longer the feminine gods, but the well-known testosterone gods Donar (Thor), Wodan (Odin), and the typical Frisian god Foseti, also named Forseti, probably worshiped at the Frisian red island Heligoland at the North Sea. But goddesses existed too, of which Freyja was the most important in the region. One of the pre-medieval superstitious practices that had survived, is digging grooves or furrows.

Proof of this pagan practice in the Early Middle Ages is archived in the devotional Vatican. It is the Codex Palatinus Latinus 577. A book that contains the Indiculus superstitionum et paganiarum ‘Small index of superstitious and pagan practices’, and also includes the fascinating Baptismal Vow of Utrecht. It was written in the year 742 or 743, opinions differ, and probably used by Saint Boniface to christianize the Saxons and the Frisians in the eighth century.

early-medieval so-caled Stabidole, Heiloo in province Noord Holland

A relatively obscure idol appears in the vow, namely the god Saxnot. Maybe worshiped by the Frisians too, for the Frisians are by and large of Saxon origin (check out our post Have a Frisians Cocktail for more background about the origin of the Frisians). The Baptismal Vow of Utrecht is also curious, since it is not written in Latin but in an odd mixture of among other Old Saxon, Old Frisian and Old Low Franconian. We can compare it with the fusion languages of Papiamento and Patois of today. Picture how the Anglo-Saxon bishop Boniface baptized pagan Saxons and Frisians reciting this creole vow with, of course, a solemn expression on his face:

Forsachistu diobolæ? Et respondeat: ec forsacho diabolæ.

End allum diobolgeldæ? Respondeat: end ec forsacho allum diobolgeldæ.

End allum dioboles uuercum? Respondeat: end ec forsacho allum dioboles uuercum

and uuordum thunær ende woden ende saxnote ende allum them unholdum the hira genotas sint.

Gelobistu in got alamehtigan fadær? Ec gelobo in got alamehtigan fadær.

Gelobistu in crist godes suno? Ec gelobo in crist gotes suno.

Gelobistu in halogen gast? Ec gelobo in halogan gast.

Do you forsake the Devil? And the answer must be: I renounce the Devil.

And all Devil’s money [sacrifices to the devil]? The answer must be: And I forsake Devil's money.

And all Devil’s work? The answer must be: And I forsake all Devil’s works

and words Donar and Wodan and Saxnot and all demons who are their followers.

Do you believe in God the Almighty Father? I believe in God the Almighty Father.

Do you believe in Christ, God's Son? I believe in Christ, God's Son.

Do you believe in the Holy Spirit? I believe in the Holy Spirit.

3. The indiculus 'index' itself

This index is without the book, which has been lost. So, we have to judge the book by its cover this time. The index is written in Latin, although it contains a few Germanic words that they could not translate into Latin speech back then, namely nimida (i.e. the sanctuary in the forest, and maybe the same spot Tacitus identified), nodfyr (translated as 'holy fire', and considered the oldest Low Franconian/Old Dutch word survived too) and yrias (a kind of run). In total 30 rituals and pagan practices are listed.

  1. de sacrilegio ad sepulchra mortuorum ‘of sacrilege at the graves of the dead’

  2. de sacrilegio super defunctos i.e. dadsisas ‘of sacrilege to the dead, i.e. the death feast’

  3. de spurcalibus in Februario ‘of swinish feasts in February’

  4. de casulis i.e. fanis ‘of small buildings, i.e. shrines’

  5. de sacrilegiis per ecclesias ‘of sacrilege in churches’

  6. de sacris silvarum, quae nimidas vocant ‘of sanctuaries in woods they call nimidas’

  7. de his, quae faciunt super petras ‘of those things they do upon the rocks’

  8. de sacris Mercurii vel Iovis ‘of the sanctuaries of Mercury and Jupiter’

  9. de sacrificio, quod fit alicui sanctorum ‘of the sacrificial service for some saints’

  10. de philacteriis et ligaturis ‘of amulets and knots’

  11. de fontibus sacrificiorum ‘of fountains of sacrifices’

  12. de incantationibus ‘of incantations’

  13. de auguriis vel avium vel equorum vel bovum stercora vel sternutationes ‘of auguries from manure from birds, horses or cattle and sneezing’

  14. de divinis vel sortilegis ‘of diviners or sorcerers’

  15. de igne fricato de ligno i.e. nodfyr ‘of the fire made from the friction of wood, i.e. nodfyr’

  16. de cerebro animalium ‘of the brain of animals’

  17. de observatione pagana in foco vel in inchoatione rei alicuius ‘of the observance of the pagans on the hearth, or at the start of any business’

  18. de incertis locis, que (quae) colunt pro sanctis ‘of undetermined places they worship as sanctuary’

  19. de petendo, quod boni vocant sanctae Mariae ‘of bed-straw which good people call Saint Mary’

  20. de feriis, quae faciunt Iovi vel Mercurio ‘of feasts they hold for Jupiter or Mercury’

  21. de lunae defectione, quod dicunt vince luna ‘of the lunar eclipse they call vince luna’

  22. de tempestatibus et cornibus et cocleis ‘of creating storms and horns and snail shells’

  23. de sulcis circa villas ‘of grooves encircling houses’

  24. de pagano cursu, quem yrias nominant, scis[s]is pannis vel calciamentis ‘of the pagan race they call yrias, with torn clothes and shoes’

  25. de eo, quod sibi sanctos fingunt quoslibet mortuos ‘of this, what they describe as a holy death’

  26. de simulacro de consparsa farina ‘of the idol made of dough’

  27. de simulacris de pannis factis ‘of idols made from torn clothes’

  28. de simulacro, quod per campos portant ‘of the idol carried through fields’

  29. de ligneis pedibus vel manibus pagano ritu ‘of wooden feet and hands in a pagan rite’

  30. de eo, quod credunt, quia femine(ae) lunam comende(n)t, quod possint corda hominum tollere iuxta paganos ‘of this, which they believe, that women command the moon, so they can take out people’s heart according to the pagans’

Practice number 23 is the one about grooves or ditches, often translated as furrows. Since the index is very general, it is difficult or impossible to really understand what the superstitious rituals actually did look like, and what their purpose was. Nevertheless, it gives us a rare insight into some of the pre-christian practices of the Saxons and the Frisians during the Early Middle Ages.

Although not in the terp region, the practice of grooves in ritual practices has been found in a clay mound at present-day town of Katwijk in province Zuid Holland as well. This terp was actually a burial ground, more or less during the Roman Period. Here circular grooves have been excavated, encircling cremation graves. The cemetry of Oosterbeintum in province Friesland also has circular ditches. From other burial grounds from the Iron Age in the Netherlands we know that these burial grounds were considered transitional places between earth and the world of spirits. The grounds were often encircled by furrows. More in general, Late Bronze Age interments often in an urn, where placed in a pit surrounded by a circular or oblong ring-ditch (Waterbolk 1977).

The (religious) practice or ritual of making grooves did not stop in the Middle Ages. Churches in Westphalia, Germany and in the Netherlands have grooves scratched into stones on the exterior of ca. 25 cm long and 5 to 6 cm wide and deep. This practice continued well into the twentieth century. You can find them for example at the southern door of the church of the village of Loppersum, on sarcophagus in the church of the village of Termunten, in the Saint Boniface church of the village of Wehe-Den Hoorn, and on a tomb lid of the former cloister of Ter Apel. All these examples are found in province Groningen. Also, the teeny tiny terp village of Jannum in province Friesland has lids of sarcophagus and altar stones with grooves. But in many more places in the Netherlands grooves can be found, like the churches in the towns of Aardenburg, Goes, Naarden, Kortgene and Rhoon.

Mostly these grooves are made in sandstone and the gravel that came of it was often dissolved in water and used to cure illnesses. By the way, not only gravel was used, but pulverized human bone as well. This latter practice was documented by historian Gregory of Tours in the sixth century.


Chinese Medicine

Only recently the Chinese government legalized rhino and tiger bone for medical purposes. If people still believe in the medicinal remedy of bone, would it not be better if they return to the old practices, and use human bone again or the gravel of holy stones again?


Stones as such, besides grooves carved in them, in the landscape of Frisia were a scarcity, and perhaps for that reason often have a spiritual or religious meaning as well. Think of the stone Archbishop Rimbert of Bremen prayed upon to ask for God’s help for the Frisians to defeat the Vikings near the town of Norden, Ostfriesland. Prayers that were being answered, by the way. Read our post A Theelacht: what a great idea! to learn more about this mircale, because they succeeded. The stone can be found at the Liudger Church of Norden. But also think of the Devil’s stone at the village of Godlinze, the stone at the village of Holwierde, the stone at Westerklief at the former island of Wieringen, and the stones on the graveyard of the village of Rinsumageest. All shrouded with stories. Stones also frequently appear in sagas, like in the East-Frisian sagas of Der Blutstein in Stapelmoor, Die Steine von Osteel, Der Marienstein in Stapelmoor, Der Hilgenstein, and Der Vosskutt in Burhafe.

4. Conclusion

After reading all of the above, from human skull cups and amulets, to inhumations under house floors, bones placed in grooves and the Indicules, we leave it now to your own imagination what the world and people looked like from the Roman Period to the Early Middle Ages. Knowing, of course, a lot had changed between these two eras.

Baby, just sing about the groove (Sing it)

Note 1 - The Roman gods (as mentioned in the pagan practices number 8 and 20 of the indiculus) Jupiter and Mercury were replaced in the Germanic religion by respectively Donar/Thor and Wodan/Odin. After Christianization, these gods were replaced by respectively the apostle Saint Peter and the archangel Michael.

Note 2 - Check out more heathen (funeral) practices, some of which even have survived at the former salt marshes to this very day, in our post How to bury your mother-in-law?

Suggested music

Deee-Lite, Groove Is in the Heart (1990)

Further reading

Coulthard, S., A Short History of the World According to Sheep (2020)

Eijnatten, van J. & Lieburg, van F., Nederlandse religiegeschiedenis (2006)

Fernández-Götz, M. & Roymans, N., The Politics of Identity: Late Iron Age Sanctuaries in the Rhineland (2015)

Fontijn, D., Economies of Destruction. How the systematic destruction of valuables created value in Bronze Age Europe c. 2300-500 BC (2020)

Groenewoudt, B., Beek, van R. & Groothedde, M., Christianisation and the Afterlife of Pagan Open-Air Cult Sites. Evidence from the Northern Frankish Frontier (2016)

Hines, J., Religion and conversion amongst the Frisians (2021)

Hunink, V., Tacitus. In moerassen & donkere wouden. De Romeinen in Germanië (2015)

In Pago Wirense, Legends and Folklore on Wieringen (website)

Knol, E., et al, The medieval cemetry of Oosterbeintum (Friesland) (1996)

Laan, van der J., De bijzondere houten voorwerpen uit de opgravingen in Ezinge (2016)

Lendering, J., Hludana. Livius.org (2004)

Mees, K., Burial, Landscape and Identity in Early Medieval Wessex (2019)

Nicolay, J., Het kweldergebied als cultuurlandschap: een model (2015)

Nieuwhof, A., Dagelijks leven op terpen en wierden (2018)

Nieuwhof, A., Eight human skulls in a dung heap and more. Ritual practice in the terp region of the northern Netherlands 600 BC – AD 300 (2015)

Nieuwhof, A., Graven en botten. Menselijke resten in Ezinge (2014)

Nieuwhof, A., The Frisians and their Pottery: Social Relations before and after the Fourth Century AD (2021)

Oneindig Noord-Holland, Een idool van hout (2012)

Prummel, W. & Hullegie, A.G.J., Bewerkte voorhoofdsbeenderen van pasgeboren kalveren uit drie terpen (2016)

Renswoude, van O., De weg naar een nieuwe ee (2021)

Renswoude, van O., Hof, harg en hal: het heten van heiligdommen (2021)

Renswoude, van O., Hoge ouderdom op de Veluwe (2021)

Renswoude, van O., Woen bij de Friezen (2021)

Saupe, H.A., Der Indiculus Superstitionum Et Paganiarum. Ein Verzeichnis Heidnischer Und Aberglaubischer Gebrauche Und Meinungen Aus Der Zeit Karls Grossen (1891)

Schuyf, J., Heidense heiligdommen. Zichtbare sporen van een verloren verleden (2019)

Siefkes, W., Ostfriesische Sagen und sagenhafte Geschichten (1963)

Tuin, B., Rondslingerend menselijk bot? (2015)

Tuuk, van der L., De Friezen. De vroegste geschiedenis van het Nederlandse kustgebied (2013)

Visser, A., Scheppers van aarde (2016)

Waterbolk, H.T., Walled enclosures of the Iron Age in the North of the Netherlands (1977)