So how did the Vikings sail these vast distances in an age without electricity, solar, wind, steam power, or even an internal combustion engine? 

The answer was blowing in the wind...

A sacred part of society

If you look at the Scandinavian Peninsula on a map, you will notice that it is surrounded by vast seas and oceans. The humble ship has played a central role in Scandinavian culture for thousands of years. 

Given the geography of Scandinavia – dense forests, a huge mountain range running down the "spine" of the peninsula, and easy access to the sea – the ship has been the preferred (and most convenient) mode of transport until, at least, the railway arrived in the mid-19th century CE.

The first evidence we have of ships in Scandinavian societies is from the Nordic Bronze Age (c. 2000 - 500 BCE), mostly of stone engravings. In fact, several thousand of these petroglyphs have been uncovered all throughout the entire peninsula. 

As time progressed, the ship, aside from its functional role as a mode of transport and a means to procure food, took on a religious and ceremonial role, evident from about the very beginnings of the Nordic Iron Age (c. 500 BCE - 800 CE). 

The Hjortspring boat, built around the turn of the 4th century BCE and uncovered in a bog in Demark, was discovered along with a horde of grave goods as well as a literal menagerie of sacrificed animals and humans.

Unique boat design

By the dawn of the so-called "Viking Age" (c. 793 - 1066 CE), peoples in Viking societies across the Scandinavian peninsula had perfected the design of what is generally known as "Viking ships." 

Essentially, unlike ships and boats constructed in other parts of Europe, these were "clinker built." This type of construction is when overlapping planks are riveted together. 

The key difference in this construction method is that it makes the vessel lighter and more seaworthy than other vessels employing different methods. 

From the smallest auxiliary vessel to the largest warship, carrying up to 100 warriors, the clinker method was a key military and technological advantage of Viking societies.

The clinker method of construction made the vessel more streamlined and, thus, hydrodynamically more efficient than other methods, meaning a greater nautical speed. 

Furthermore, this construction created a vessel that was more flexible, meaning the ability to quite literally roll with the heavy waves of the North Sea or the Atlantic Ocean.

Crews and muscle power varied depending on the size of the vessel. The smallest "Viking ship" was the færing, a mere rowboat with two pairs of oars. 

It is estimated that the largest longship, used for war, the bússa, had as many as 34 rowing positions on each side. Yet most larger Viking vessels also had a mast to which a sail could be attached.

It has been estimated that it took as long as two years for a Viking sail to be made on a smaller boat. Photo: Michael Rosskothen / Shutterstock

Sails made the ships seriously fast

If we look at the early medieval sources, from a range of societies and civilizations, all have one thing in common: they could not believe just how quickly the Vikings appeared, wreaked havoc, then disappeared. 

This is due to their vessels. As mentioned, not only did they have a crew of warriors rowing but, when the winds were favorable, a sail could be flown, and the vessel could rely on the use of wind power. 

This made it possible for the vessels to travel long distances across heavy seas and oceans. People from Viking societies traveled to a wide range of diverse places thousands of miles from their home, including modern-day Canada, the heart of the Abbasid Caliphate in Baghdad, Greenland, and the shores of northern Africa.

It took, however, an entire community to literally make just one Viking sail.

A communal work

The fragments of Viking sails that archaeologists have uncovered show that these sails were made of two different materials: flax and wool. 

Each has distinct advantages and disadvantages, but the commonality is that either method was not only time-consuming but needed a significant amount of people power.

Flax is extracted from the skin of a flax plant. This fiber makes a perfect sail that is strong yet relatively light. However, the use of this fiber took time. 

This was not seen as an efficient material for the sails, as the plant had to be tendered and ripened before the fiber could be extracted. 

Furthermore, Scandinavia has a notoriously "fickle" (let's be nice here, there are other words that could be used here) climate, and the weather is not that conducive for the growth of plants or crops. 

After collection, the fibers then had to be worked over for them to be ready to weave the sail together. Finally, as it was a plant fiber, and thus organic, rot set in relatively quickly, making them unfortunately readily disposable.

Wool was the mainstay of Viking society as it provided great warmth and was easy to clean. However, compared to flax, it may be heavier in weight but has greater elasticity and does not rot. 

It is also harder to treat for the harsh climatic conditions of the Viking world. The use of wool for a sail quite literally involved the whole community.

According to some theories, population pressure and decreasing amounts of land for farming may have "pushed" people in Viking societies outward to find land. Photo: Michael Rosskothen / Shutterstock

Wool was central to Viking society and expansion

The small amount of arable and pastoral land on the Scandinavian Peninsula has been suggested, by some academics, as a key "push" factor in the Viking expansion from the 8th century CE. 

With population pressure and ever-decreasing amounts of land for farming, people in Viking societies may have been "pushed" outward to find land. 

A flock of sheep was needed to provide enough wool to make a sail. This required a significant amount of both land and people. 

Wool production became an important collective focus of Viking societies as families banded together to produce enough wool to make a sail. It has been estimated that about 400 sheep were needed to provide the required amount of wool for the sail of a Viking ship.

Selective breeding was used to ensure sheep with sturdier hardy wool, perfect for the climatic conditions of the harsh North Atlantic world. 

These sheep, found on the islands of northern Scotland, the Faroes, Norway, and Iceland, provided the perfect wool. They had a sturdy outer layer, perfect for waterproofing, while the inner layer was perfect for insulation.

The 6-step process for making a sail

Scholars have pointed to a 6-step process in turning wool into a Viking sail:

1) Rooeing: Families reared the sheep and, in springtime, "rooed" the wool. Sheep naturally shed their wool in springtime, so families simply pulled the malting wool from the sheep rather than shearing it.

2) Treating: The wool was divided into two layers and then treated, with a little fish oil, differently.

3) Spinning: The wool was then spun, mostly by women. This was a laborious process as two different wools had to be spun to produce different yarns that complemented each other. Due to the difficulty of the process and the needed dexterity, a high level of skill was required.

4) Weaving: After the wool was spun into yarn, the yarn was then weaved.

5) Soaking: The fabric would then be soaked in water and pressed together to create a large lump of material. This method was done by placing the fabric near a tideline and weighed down with stones. It was then stretched into a square and dried.

6) Final treatment: Finally, the fabric was treated with a coat of horse oil to waterproof it and fill in any gaps in the weave.

It has been estimated that it took as long as two years for a Viking sail to be made on a smaller boat, whilst for a Viking warship, it could take as long as half a century! 

However, the high quality and sturdiness of the sail ensured that it could last for multiple decades.

For more on Viking ships, please visit the Danish Viking Ship Museum website, available here.

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