• Hans Faber

The United Frisian Emirates and Black Peat


In this post we will explain that the Frisian lands might as well be named the United Frisian Emirates. Of course, there are some differences with the modern United Arab Emirates. The Emirate Arabs have camels and goats. The Frisians have cows and sheep. It is hot and dry, instead of wet and cold. And the sea they live at is named Persian Gulf and not North Sea. But here the differences stop. Full stop.


For long the Arab tribes in the Persian Gulf lived off trade, copper, pearls and, as every sea-side people, on piracy. In the year 1971, these desert principalities formed the federal state United Arab Emirates. It were in total seven emirates that joined the federation, namely: Abu Dhabi, Ajman, Dubai, Fujairah, Sharjah, Ras-al-Khaimah and Umm-al-Quwain. All seven Emirates are located at the southern shores of the Persian Gulf.


This is no different from medieval Frisia. In the High Middle Ages, Frisia was a federation of also seven independent republics. The Seven Sealands as they called themselves. These were: Westfriesland, Westergo, Oostergo, Stellingenwerven (variable including province Drenthe), Ommelanden (variable with the city Groningen), Ostfriesland, and Butjadingen together with Riustringen and Wangerland. These Seven Sealands were united in the so-called Upstalsboom treaty meaning 'treaty of the high tree'. All Seven Sealands were located at the southern shores of the North Sea. Read our post Upstalsboom: why solidarity is not the core of a collective to learn more about this early federation.


Concerning piracy? Yes, the Frisians did that too. One might even argue that the Frisians are a result of a long-standing piracy culture that started in the Late Antiquity and continued into the High Middle Ages. Read for example our posts It all began with piracy and also Yet another wayward archipelago.


The United Arab Emirates have a liberal, economic policy. The federation created economic and tax-free zones to attract international investment and trade. A worldwide trade network has been established. Also through air with big commercial airlines like Emirates, Etihad and FlyDubai. Early-medieval Frisia more or less invented free trade. Frisian merchants belong to the founding fathers of economic liberalism. Yes, free trade, free(dom) and Frisian became even synonyms during the Early Middle Ages. Their international trade networks were maybe not global, but certainly the biggest of northwestern Europe. Frisian seafarers transported their trade over seas and over rivers from Paris to Stockholm and from Trier to London. Read also our post Porcupines bore U.S. bucks to get a fuller picture of these egocentric sea traders.


Last but not least in the comparison, almost sixty years ago oil was found in the area what is now known as the United Arab Emirates. Since then, the wealth of the Gulf became unparalleled. At present (2019) the United Arab Emirates are the eighth biggest oil producer in the world with a production more than 3,000,000 barrels per day. One barrel is almost 160 litres of oil.


For medieval Frisia it was the same. It was not oil, though, but another fossil fuel, namely peat. Some say the slowly sustainable energy because peat grows 10-15 cm over a century. Just like the Gulf Arabs, the Frisians happened to sit on organic gold. “Zwischen Watt und Moor” as they say in Ostfriesland and in Nordfriesland. From the mouth of the mighty River Scheldt in Flanders all the way up along the North Sea coast to Landkreis Nordfriesland just south of the Danish border in Germany, extensive peatlands existed. We estimate at least 25,000 square meters of peat lands. Square meters. We are not talking cubic meters, yet. Easily two metres deep. It were the Frisians who started to exploit these peatlands commercially and, thus, systematically. It supplied the Frisians, and later the Dutch and Germans, with much wealth. From the Early Middle Ages well into modern history. Maybe it was this economic wealth that was the real foundation of the Republic of the Seven United Netherlands, the birth of the Netherlands. We will come back to it further bellow. And the number 7 keeps popping up…


By the way, the fact the peatlands of (former) Frisia have been fully exploited, means that in the process huge amounts of carbon have been unlocked and released into the atmosphere. Wetland ecosystems are, in fact, one of the most efficient carbon sinks. As far as we know, no scientific estimations have been made yet about the amount of carbon that has been unlocked throughout the centuries of peat exploitation in (former) Frisia, from Ostend in Flanders to Misthusum in Denmark. We estimate that it could have been around three billion tonnes of carbon. Voilà, the Frisian's climate debt and contribution to global warming, melting glaciers and still rising sea levels.

Black Peat

We are not going to debate in this post about Black Pete climbing through chimneys and all, to deliver gifts to kids and that way becoming black of soot. No, we will go more in depth about commercial peat exploitation in medieval Frisia, and what it meant for the landscape and even for the Frisian identity.

In the year 961 or 962, the Hispano-Arabic traveler Ibrahim ibn Ya’qub from Tortosa in Spain visited Frisia. One of the things he noticed, was that the land was soaked in salt, and therefore unfit to bring forth any crops. He further described shepherds who dug out blocks of a kind of mud, dried and then burnt it. Of course, this was the elegant process of peat cutting. What the purpose was of burning the blocks of soil, early hiker Yaqub did not tell us. Or, maybe he simply did not understand what he saw.


According to archaeological research, peat cutting started in the coastal zones of what is now the coast of Flanders up to the River IJ, near Amsterdam in the Netherlands, during the Early Iron Age between 700 and 500 BC. The oldest traces of peat cutting in the Netherlands have been found in Westmade polder (polder meaning embanked land) between Rotterdam and The Hague. Calculations are that ca. 40,000 cubic meters of peatland has been dug out here between 800 and 400 BC.


Peat as fuel was (also) needed for commercial production of sea salt. The North Sea with a sodium-chloride percentage of ca. 3.5 provided an endless supply of salt. Of course, if you have saline peat, you can extract salt out of that too. But, most probably this latter type of commercial salt production was only introduced in the Early Middle Ages. Before that, peat was solely or primarily used as fuel. Fuel to produce, as said, sea salt at first. Later, during the Roman Period, this fuel was also used for the production of allec 'fish sauce' and related garum, and for the production of lime needed for stone constructions. Perhaps salt was needed for tanneries too. Sea salt was being produced in the Early Iron Age at for example De Panne in Flanders and at Monster in the Netherlands.


Large-scale peat cutting activity during the Roman Period already had its effect on the environment. Big floods in the Flemish coastal zone and in province Zeeland in the Netherlands during the Late Roman Period, were a consequence of lowered land after peat had been dug out. This next to local combinations of marine transgression, a more high-energetic North Sea due to sedimentation, and the slow defrosting process, thus shrinking process, of the deeper soils since the last ice age. A defrosting process known as the Great Watering which was on its height in the fourth century.


To date, no archaeological indications exist salt was being produced commercially above the River IJ, nor in the terp (i.e. artificial dwelling mound) regions of Germany and of the Netherlands before the Early Middle Ages. Also, peat cutting started here only at the end of, or after, the Roman Period. Besides, dried dung provided the terp dwellers of the north with fuel for heating and craft already. So, maybe there was lesser need to cut peat large-scale. At the salt marshes of northwestern Germany and of the Netherlands cow-dung was available in abundance. Above that, dung was not needed to fertilize the land, since tidal marshlands were fertilized through regular flooding by the sea. Dried dung as fuel is by the way exactly how it is still being used to heat houses and trekking lodges at higher altitudes in Nepal, and where trees are scarce too. In the treeless, barren Nordfriesland, the practise of cow dung being dried for fuel by Warft (i.e. terp) dwellers of e.g. Hanswarft, Germany continued well into the '50s of the last century. A region where people live at the tidal marshlands unproteced by dikes to this day.


Reclamation of peatlands in West Frisia, i.e. the area between the coastal zone of Flanders and the former River Vlie in the Netherlands, started near the current town of Medemblik in the region Westfriesland. It is assumed these activities mainly focused at creating arable land. This meant draining the wet peat soil with ditches and canals. This in turn led to a process of oxidization of peat, and of simply drying out and crumbling of the soil. Therefore, the soil started to settle, to shrink, and became vulnerable for floods. Also, many lakes emerged in these lowered lands. Lakes itself eat and carry away land too, if you do not protect lake shores by men. And, the larger the surface of lakes and sea inlets becomes, the bigger the volume water becomes that is set into motion during storms, and thus the greater the force in swallowing land. Gullies like the Marsdiep, Vlie and Jetting pushed more and more water with great force onto the shores (Schroor 2015).


The starting pistol for this degradation process was fired around the turn of the eighth and ninth centuries. When in the last decennia of the twelfth century also temperatures rose leading to more rainfall and a higher frequency of storms, most of the peatlands disappeared and turned into either (inlet) sea or lakes. This process was locally accelerated because of the production of salt.


These early-medieval reclamations stimulated, or possibly even caused, the widening of the River Vlie that flowed east of Medemblik, connecting lake Almere with the Wadden Sea and North Sea. This process in turn had all sorts of ecological, house-of-cards-falling consequences, including contributing to the process of lake Almere turning into a full-fledged inland sea, the Zuiderzee 'southern sea'.


area De Moer Wardt, map by Christiaan sGrooten (1573)

Another activity that helped to create the Zuiderzee, was the exploitation of the Moer Wardt or Moerwaard. This was an salt-marsh area south of island Vlieland, consisting of peat covered with sea clay. Because this area was regularly flooded by the sea, the peat of was rich of salt. Today, the name Waardgronden of this part of the Wadden Sea still remind of this former land. From medieval chronicles we know this area was heavily commercially exploited and canals were dug, like the Monnikensloot canal, also called De Pan, which possibly refers to the production of salt. The Jetting was another canal, connecting Harlingen with the Vlie. These high-medieval ditches and canals enhanced the emergence of sea gullies and widen the western part of the Wadden Sea. Possibly, salt was isolated from the ashes of burned peat on the Moerwaard itself, and then transported to the mainland, among other to Harlingen. At the end of the twelfth century, the western Wadden Sea had fully merged with lake Almere (Schroor 2015). Needless to say, this whole lake-turning-into-sea thing has meant giant, giant loss of land.


During the ninth century, peatlands were claimed by the water south and west of the town Medemblik, including the peatlands of the area De Beemster. De Beemster became a big lake, was reclaimed by men from the water in the early-seventeenth century again, and is now a Unesco-listed heritage site. In the eleventh century, the region of Spaarnwoude followed. The result was that, around 1200, all peatlands of West Frisia north of the River Oer-IJ, i.e. most of present-day province Noord Holland, had been cultivated or had been lost to the many emerging lakes. As said, even a complete new inland sea had emerged due this cultivation. Read our post In debt to the beastly Westfrisians to learn more about the early history of the grand dame Medemblik.


Also, at the terp region opposite to the town of Medemblik, on the other side of the River Vlie, peatlands were being exploited. Here, peat cutting and salt extraction out of saline peat took place. This started in the eighth century. A bit later, the terp region of Ostfriesland followed too. Archaeological research in the northeast of province Friesland revealed heaps of burned ashes with a diameter of up to twenty-five meters and two meters thick. Production of salt out of peat was at its height in present-day provinces Friesland and Groningen and in Ostfriesland during the eleventh to fourteenth centuries. Again, much loss of land happened during these centuries. Think of the bays of Lauwers, Dollart, Jade etc. All bays east of River Vlie emerged or enlarged in this period.


Medieval testimonia of Frisian salt production activity have been documented in writing too. In the year 775 or 776, the abbey in Lorsch in Germany received as a gift seventeen culinas ad sal faciendum. These were ‘salt kitchens’ situated on the island of Schouwen between the River Scheldt and a water called Sonnemare. Sonnemare seems to be the border between the dominium of Voorne and modern province Zeeland. Culinas were the buildings or sheds for salt boiling. In 877, the abbey of Saint Gertrud in Nivelles in Belgium possessed in Frisia terram et mancipia ad salem. Charles the Bald ceded these lands to the abbey of Saint Gertrud. In 897, this property was confirmed as in Fresia terra ad sal acquirendum, and must have been located somewhere in current province Zeeland or in coastal Flanders. That province Zeeland was an area where salt production took place in early ages, is further known from a trader from Trier in Germany whose ship was loaded with salt. This was documented in the late sixth century already (Tuuk 2021).


 

Salt March of Ghandi


And the history of human kind is a history of salt. When India was still a colony of Britain, the British controlled the salt production and export. No-one had the right to trade in salt and no one had the right to produce salt, not even for personal use. Instead, salt was taxed. And it was Ghandi who decided to walk to the coast in 1930. A hike of 390 kilometers. To slowly walk from Sabarmati Ashram to the salt marshes of Dandi. A protest against the salt taxation and against British occupation. The famous Salt March.

 

Peat cutting and salt production was not only along the Dutch and Flemish coast, i.e. West Frisia and Mid Frisia, and in region Ostfriesland a commercial activity. Also in Nordfriesland, south of the Danish border. In the Early Middle Ages, Frisians, probably from Ostfriesland, migrated to Nordfriesland and introduced their skills to extract salt from saline peat. The medieval historian Saxo Grammaticus wrote in his Gestae Danorum 'deeds of the Danes' of 1160 that the North-Frisians cooked salt out of clods. Read also our post Beacons of Nordfriesland about the colonization of Nordfriesland. Famous is the story of the prosperous town of Rungholt. A rich town thanks to commercial salt production. It, however, had to pay a heavy price for digging out and burning so much peat. In the year 1362, Rungholt together with his inhabitants disappeared overnight in the waves of the dark-green sea during the Saint Marcellus’ flood. Read our post How a town disappeared overnight.


Frisians started to reclaim peatlands more inland too. In the twelfth century, Frisians colonized a sandy ridge within an extensive peat area which is known today as Saterland in the northwest of Germany. Today, this isolated community consists of four villages with ca. 15,000 inhabitants. These are the villages Strücklingen (Strukelje), Ramsloh (Roomelse), Sedelsberg (Seedelsbierich) and Scharrel (Schäddel). Later, the town of Friesoythe was added to the municipality as well. Saterland is the only area where the East-Frisian sub-dialect Seeltersk has survived, although the odds for its future survival are exceptionally grim. Only about a thousand speakers are left to date. Check our web page Language to pick up some words of Seeltersk.

Let’s turn to West Frisia again, the area comprising of present-day provinces Noord Holland, Zuid Holland and Zeeland, and parts of province Utrecht and the coast of Flanders as well.


Commercial peat cutting in West Frisia had far-reaching consequences. Not only on the environment, but also on the cultural identity. From the tenth and eleventh centuries, the counts of West Frisia started with the reclamation and cultivation of the extensive peatlands of what is today more or less the province Zuid Holland and parts of the province Utrecht up to the Utrecht Hill Ridge. The latter is a push moraine from the Middle Pleistocene glacial period.


The way the Frisian counts approached the reclamation was innovative for that time. These revenues became an important base of power of the counts to gain more independence, and thus eventually the rise of Holdland or Holtland, later corrupted into Hollant and Holland. And, since Holland was the driving force to become independent from Spain, brown gold played a pivotal role in the emergence of the Netherlands. With the counts of Holland being the oil sheikhs of the Wadden Sea. The innovative approach became known as the Great Reclamation. It was that successful, that the concept was exported at the beginning of the twelfth century to peat areas of both bordering the River Weser around Bremen and bordering the River Elbe around Hamburg. It even led to several settlements in the Bremen-Hamburg area. Settlers locally known as Frisians and Holler, the latter meaning ‘those from Holland’. This so-called cope contract concept was exported to the British Isles and other parts of Frisia too (Van Doesburg 2019).


By the way. The names of the farmers who exported the concept of cope contracts to the marsh areas around Bremen and Hamburg have been documented. They were Helekinus, Arnoldus, Hiko, Fordolt, Referic and Heinricus who emigrated in the year 1113 to this region and agreed with the local bishop a cope contract. More migrants from Frisia and Holland came in the decennia that followed.


Below we will zoom into the cope type reclamation of the peatlands of province Zuid Holland and Utrecht. It is, however, instructive to know that in other areas different types of reclamation existed, like the drifting settlements in provinces Noord Holland, Friesland and Groningen. Here, parallel with the quarrying process, villages steadily moved inward peat areas. Sometimes leaving their churches and graveyards, often situated on handmade mounds or terps, behind. The reason why villages were adrift, is under scholary debate. Probably, it had to do with sinking soils and rising groundwater, and with growing distances between the farmsteads and the newly created arable land (Van Doesburg 2019). Another factor probably was that the cope type reclamation was designed and directed top-down by feudal institutions, as we will see in a moment, whereas this was not the case in northern Frisia where these instituations were completely absent.



How was the Great Reclamation organized?

The Great Reclamation started in the tenth century and was completed around 1300. It started at the peatland villages Rijnsaterwoude and Esselijkerwoude in modern province Zuid Holland. The counts of West Frisia issued lots to farmers of which they were allowed to dispose of freely. These lots measured thirty roe or roeden wide (between 110-115 meters) and six or twelve voorlingen long (respectively around 1,275 and 2,550 meters). These lots were called a cope.


The measurements of a cope were a practice of the feudal system already. The standard thirty roeden by six voorlingen, also called a morgen, generally was considered to be enough for one family to live off. The word voorling is related to the Dutch word voor meaning furrow, also compare the Mid-Frisian word fuorge. A voorling was the distance during plowing after which the beast of burden had to rest before turning around and plow the next furrow in the opposite direction. In return for receiving a cope, the farmer and his family had to pay an annual tax called a tijns which amounted one penny (or penning, denier, denarius etc) at first. Furthermore, these farmers were obliged to perform defensive military tasks too when called upon by the count.


This way of social organisation was different from the centuries before and from the Carolingian feudal society, where most farmers were unfree and the ‘property’ of a homestead.


With the reclamation of the peatlands, the amount of arable land increased as well. This led to a surplus of crops and therefore stimulated the introduction of trade and the money economy in the rural areas in the twelfth century. The counts were confronted with increasingly richer farmers whilst their incomes were pretty stable. From the twelfth century, the tax for a cope was raised, from one denarius to four denarii. It made count Floris II, known as Floris the Fat for no reason, filthy rich. Fatboy Floris was known as someone who surpassed his forefathers in power, in prestige and in wealth. And, probably in body-weight, we add.


At this stronghold, the Fladertingi 'people of Vlaardingen' demanded toll from passing ships. This illegal toll threatened the trade between the trading town of Tiel with England. Furthermore, the subversive actions of the West-Frisian counts meant a fall in toll revenues at Tiel. This toll was held by the bishop of Utrecht (Van der Tuuk 2021). Tiel was located upstream on the banks of the River Waal. The conflict that arose between the two eventually led to the battle of Vlaardingen in 1018, which was won by the West-Frisian count Dirk III. Revenge for the Frisians, at last, after the lost Battle at the Boorne in 734.


 

Merwede


The word Merwede originates from 'meriwidu' meaning something like 'dark wood'. Compare 'meri' with murky and 'widu' with wood.

 

Also, this massive reclamation and cultivation of the interior came with a price which amounted more than the tijns tax, namely the change of identity of the Frisians living in West Frisia. Social and landscape related organization and identity, are closely intertwined. The massive reclamation and cultivation led to urbanization which attracted large numbers of people from outside. This must have led to a situation of different dialects of Frisian (also called Coastal Dutch in linguistic classification), Western, Central and Eastern Dutch. In such a situation a koine can arise. A koine is a hyperdialect. A blend of all the different dialects to function as the new common speech of the melting pot of peoples within a short period of time.


From ca. 1050 onward, Frisian placenames started to disappear in West Frisia and were replaced by Frankish ones (Cordfunke 2018). Read our post Take a virtual hike through Zuid-Holland and Utrecht to check out the Old-Frisian place names in these two provinces, or check out the real name of Brooklyn Bridge in New York. Not only the whole top soil was scraped away a few meters deep, similar to the Canadian tar sands of today, together with all its archaeological history, it also led to the phenomenon of roaming villages. Villages wandering from one place to another after all the peat was dug out and sold. It was a true social paradigm shift.


The Frisian character of the people disappeared and it was the already mentioned count Floris the Fat (see his, possibly somewhat too slender, image below) who in the year 1101 no longer named himself count of Frisia but Florentius comes de Hollant ‘Floris count of Holland’. The same year, by the way, that the Saxon Henry the Fat, newly appointed margrave of Frisia east of the River Lauwers, was murdered by Frisians. His life came to an end near present-day Norden in the district Aurich. Henry the Fat should have been more careful in Norden, since Frisians had slaughtered an army of more than 10,000 Vikings at that same spot in 884. Anyway, re-branding himself as Floris the count of Holland was, you might say, the deathblow of Hollant being Frisian of identity. Of course, the title sheikh of Holland would have been more appropriate. Anyhow, from this time onward the Frisian language disappeared as well in West Frisia.

 

Frisia versus Holtland


The oldest reference of Holland is Holtland, used in the registers of the diocese Utrecht in the ninth and tenth centuries. The word ‘holt’ or ‘hold’ meaning (ascending) wood. These were the wooded lands on the geest soils near the mouth of the River Old Rhine, near the present-day towns Valkenburg and Wassenaar. There is a minority report of a scholar suggesting it is actually ‘hol’ and not ‘holt’ or ‘hold’ and therefore meaning low-lying land (Halbertsma 2000). Be that as it may, at the end of the eleventh century, the name Holdland or Hollant surfaces, and is being used more and more to indicate the area along the North Sea coast.


In 1063, count Robert the Frisian, count of Flanders, gained influence in West Frisia through his marriage with widow Gertrude of Saxony. The counties named in this context were Holdlandiae and Fresie. Holdlandiae was what for centuries was named ‘circa horas Reni’, i.e. the areas arround the borders of the River Old-Rhine. ‘Fresie’ was what before was named ‘Westflinge’, i.e. west of the River Vlie, more or less current region Westfriesland, the island Texel, region Waterland and region Kennemerland, all part of current province Noord Holland. In the first quarter of the twelfth century, ‘Hollant’ indicates the area between the current town of Petten in the north to that of Vlaardingen in the south, including the River Meuse-Merwede region (Henderikx 2001).

 

The exception was region Westfriesland in current province Noord Holland. This region had opposed fiercely to the counts of West Frisia and the region remained Frisian in identity much longer. Until they were finally subdued to the county of Holland by force and genuine war attrocities, at the very end of the thirteenth century. To this date, the Westfrisian speech contains many elements of the former Frisian language. In the north of province Noord Holland, Frisian might have been spoken until the seventeenth century.


Floris the Fat
count Floris the Fat

Epilogue

Not only medieval Frisia was addicted to fossil fuel, namely peat. The Republic of the Seven United Netherlands, commonly the Dutch Republic, probably owed its Golden Age more to their possession of a cheap fuel than to its infamous trade with the far East. Peat was especially cheap in the Republic because transportation costs were very low as well. This thanks to a flat country intersected with thousands and thousands of canals, rivers, lakes and other water ways. Oh yes, besides to fuel, also the Atlantic slave trade was of great importance for the economy of the Dutch Republic. With slaves the Republic could produce economically products like tobacco, sugar and coffee in the West.


The addiction to fossil fuel remained in the Netherlands. Quite soon after all the peat had been dug out, a huge gas field was discovered in the ‘50s in the previous century. It was enormous and located in province Groningen, a region what used to be part of Frisia. The Dutch kept extracting gas until the soil started to collapse and earthquakes demolished houses in the poor and aging province. Recently, the central government has decided to ‘turn off’ the gas and to reimburse all the damage caused to the crumbling houses. Till now that promised money is mainly paid to smart but costly damage experts and their reports and to lawyers. Always lawyers. Both lawyers and damage experts, but also smart politicians and senior administrators, all have promised the poor and aging people of Groningen to live the rest of their lives in province Groningen, so the money meant for reimbursement will benefit the local community, eventually. Yes, development aid that will work and a brilliant way of compensation for the last five decennia of profits.


Also, the Emirate Arabs are preparing for a future without fossil fuel and have invested heavily in diversification of their economy. Maybe they picked up the lessons of medieval Frisia relatively late, but they proved to be quick(er) learners than the heirs of Frisia, the Dutch and the Germans.

 


Further reading


Boer, de D.E.H. & Cordfunke. E.H.P., Graven van Holland. Middeleeuwse vorsten in woord en beeld (880-1580) (2010)

Brandon, P. & Bosma, U., De betekenis van de Atlantische slavernij voor de Nederlandse economie in de tweede helft van de achttiende eeuw (2019)

Broeke, van den P.W., Turfwinning en zoutwinning langs de Noordzeekust. Een verbond sinds de ijzertijd? (1996)

CIA Factbook (online)

Cordfunke, E.H.P., Een graafschap achter de duinen. Het ontstaan en de vorming van het graafschap Holland [850-1150] (2018)

Dijkstra, M.F.P., Rondom de mondingen van de Rijn & Maas. Landschap en bewoning tussen de 3de en 9de eeuw in Zuid-Holland, in het bijzonder de Oude Rijnstreek (2011)

Doesburg, van J., Medieval settlement dynamics in peatland reclamations in the western, central and northern Netherlands (2019)

Geel, van B. & Borger, G.J., Sporen van grootschalige zoutwinning in de Kop van Noord-Holland (2002)

Griede, J.W. & Roeleveld, W., De geologische en paleogeografische ontwikkeling van het noordelijk zeekleigebied (1982)

Gros, F., Marcher, une philosophie (2009)

Halbertsma, H., Frieslands oudheid. Het rijk van de Friese koningen, opkomst en ondergang (2000)

Henderikx, P.A., Land, Water en Bewoning. Waterstaats- en nederzettingsgeschiedenis in de Zeeuwse en Hollandse delta in de Middeleeuwen (2001)

Jong, ‘t H., De dageraad van Holland. De geschiedenis van het graafschap 1100-1300 (2018)

Klerk, de A., Vlaardingen in de wording van het graafschap Holland 800-1250 (2018)

Kramer, E., Valse start in het Vikingonderzoek (2019)

Kurlansky, M., Salt. A world history (2002)

Lambers, J., Het geheim van de Gouden Eeuw der Republiek van de Verenigde Nederlanden. Mythen en werkelijkheid rond de turfwinning (website)

Leenders, K.A.H.W., The start of peat digging for salt production in the Zeeland region (2004)

Leeuwen, van J., Middeleeuws Medemblik: een centrum in de periferie. Archeologisch onderzoek naar de (vroeg)middeleeuwse handelsnederzetting en het oudste regionale centrum van West-Friesland in de periode 675-1298 (2014)

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

Nieuwenhuijsen, K., Strijd om West-Frisia. De ontstaansgeschiedenis van het graafschap Holland: 900-1100 (2016)

Renswoude, van O., Het woud tussen werelden (2019)

Schrijver, P., Language Contact and the Origins of the Germanic Languages (2014)

Schroor, M., Harlingen. Geschiedenis van de Friese havenstad (2015)

Tuuk, van der L., Handelaren en ambachtslieden. Een economische geschiedenis van de vroege middeleeuwen (2021)

Ven, van de G., Turfwinning in Laag Nederland in de Middeleeuwen. Een inleiding op het thema en enige aspecten uit de geologische geschiedenis van het kustgebied (1996)

Zeeuw, de J.W., Peat and the Dutch Golden Age (1978)

Zijlmans, R., Troebele betrekkingen. Grens-, scheepvaart- en waterstaatkwesties in de Nederlanden tot 1800 (2016)