Skien’s Three Oak Barrels Reveal a 17th-Century Lime Store

At a construction site in south-eastern Norway, something initially unremarkable came to light: three old barrels, half-buried in the ground. What researchers subsequently learned from them changes the way we view the history of the city of Skien and demonstrates how thoughtfully 17th-century builders handled their materials.

A discovery that takes us back to early modern construction

Skien is among Norway’s oldest towns. With a population of almost 60,000, it is now a comparatively quiet place, but it was once an important trading centre. During rescue excavations in the Torggata area, a street in the historic centre, archaeologists uncovered three substantial oak barrels.

The barrels remained in the precise location where they had been used around 400 years ago - in situ. This is a fortunate circumstance for researchers, since their position, surroundings and contents all offer clues to their original purpose. Pale, crumbly residues were found between the barrel staves: traces of lime. A roughly made wooden pestle, a type of tamper, was also lying nearby.

“The three oak barrels were not used to store beer or herring, but formed part of a sophisticated 17th-century construction-materials logistics system.”

Tests on the inner and outer layers revealed that the barrels had held slaked lime: lime that had reacted with water and was suitable for producing mortar. Following laboratory analysis, the Norwegian Institute for Cultural Heritage Research (NIKU) confirmed that this was not a chance discovery, but a deliberately created materials store.

What the old barrels contained

Lime was a key building material in the 17th century. When combined with sand and water, it produced lime mortar, which served as a binding agent in masonry and was also used for plaster. In Skien, craftspeople apparently drew the lime directly from oak barrels set below ground level.

How this building material was used day to day

• Slaking lime: Quicklime is mixed with water, triggering a chemical reaction that produces slaked lime.
• Storage: The slaked lime matures in a damp environment, often for weeks or months.
• Mixing mortar: At the building site, the lime paste is stirred together with sand and water.
• Application: The finished mortar bonds stone and brickwork or creates layers of plaster.

This is exactly where the Skien discovery becomes significant. The barrels functioned as protected reservoirs. The wooden pestle found beside them suggests that workers stirred the lime on site and worked it into an even mixture before using it. Analysis of deposits on the barrel walls points to several periods of use: lime was added, removed and replenished. In effect, the barrels operated as reusable historical “construction-material tanks”.

Underground lime storage: an intelligent response to a harsh climate

The barrels were not placed underground by accident. Researchers believe they were intentionally sunk into the ground so that their contents could be controlled more effectively. The soil around them was permeated with a lime-rich matrix, supporting the theory that the material was regularly handled there.

“Storage in the ground stabilised the temperature, prevented frost damage and kept the lime reactive.”

Temperature management was particularly important in Norway’s cold winters. If lime freezes, its structure may change, reducing the quality of the mortar made from it later. Underground storage works like a natural cellar: cool without becoming too cold, damp without becoming waterlogged. The oak barrels provided durability, while the surrounding soil supplied the necessary climatic buffer.

Researchers therefore conclude that Skien’s builders were not simply improvising, but following a clear plan for handling materials. Lime was valuable and labour-intensive to produce. Careful storage conserved resources and helped ensure the quality of walls and houses.

A town rethought after fires

Skien was repeatedly struck by major fires during the 17th century. At the time, timber houses regularly burned down in many Nordic towns. After these disasters, residents faced a pressing question: how could they rebuild - and rebuild better?

The newly excavated barrels fit precisely within this period of reorganisation. Specialists suspect that the underground lime store formed part of a wider plan to reconstruct the town in a more stable and resilient way. More masonry, more plaster and more firewalls would all have required large quantities of dependable lime mortar.

For historians, this is particularly compelling because town plans, deeds and written records reveal a great deal about property ownership and taxation, yet say little about practical construction-materials logistics. The barrels provide a rare missing piece: a location where the very mortar that bound together the houses of the rebuilt town was prepared.

What the discovery reveals about town planning

The analyses provide indications of several aspects of construction at the time:

How researchers uncover the barrels’ story

Turning a few pieces of timber and several crumbs of lime into a history of construction requires modern techniques. NIKU specialists used several methods.

• Dendrochronology: Analysing the growth rings in the oak timber makes it possible to narrow down when the trees were felled.
• Microscopy: Thin layers of lime residue are examined under a microscope to establish their composition and age.
• Geochemical analysis: Minerals and trace elements are identified to determine the origin of the limestone.
• Stratigraphy: The barrels’ position within the soil layers indicates the construction phase in which they were used.

Together, these data firmly place the discovery in the 17th century and connect it with known fire damage and rebuilding phases in the town. The barrels can therefore serve as a chronological reference point for other finds within the same layer.

Why oak barrels survive so well

Oak was considered a premium timber from an early period. It expands slightly when damp, sealing its joints, while also being hard and resistant to decay. It was therefore ideal for barrels that had to withstand lime-rich moisture. The fact that all three containers have survived so well after centuries is also due to the constant dampness and lack of air underground. Oxygen-poor environments slow down the microorganisms responsible for decomposition.

Such discoveries are not commonplace in Scandinavia, but they fit a familiar pattern. Old wooden structures repeatedly emerge in harbour areas and historic town centres, ranging from latrines and wells to ship remains. Together, they tell of an era when timber was the most important raw material and components often had a second or third use before being discarded.

What the discovery means for modern building and restoration work

For conservators of historic buildings, the barrels offer more than an intriguing detail. They provide clues about the original composition of lime mortar in the region and the conditions under which it matured. Anyone repairing an old wall in Skien today can use this knowledge to recreate mortar more closely resembling the original material.

The discovery also shows how early people began organising material cycles. Central stores, improved storage conditions and reusable containers all sound remarkably modern. Sustainability was not a term used at the time, but the economical handling of scarce resources was certainly important.

For visitors to the town, the discovery may eventually feature in guided tours or exhibitions. Seemingly unspectacular objects such as three old barrels can make history tangible: it is almost possible to picture workers 400 years ago carrying heavy wooden buckets of lime mortar to a newly raised wall, while a town rose anew from the ashes of earlier fires in the background.