|
http://www.bbc.co.uk/history/ |
| 19th-century excavations uncovered mysterious underwater structures. Explore the techniques used for building these prehistoric dwellings, and the traces left behind. |  Crannog marked by scrubby trees in Loch Lochy
|
Crannogs have always been steeped in a little mystery, as they are fairly inaccessible except to divers and boating enthusiasts.
They are artificial or modified natural islands, found in many of the lochs of Scotland and Ireland. They were built as defensive homesteads, and probably as symbols of status, from as early as 5,000 years ago, but people continued to build them, or re-build and occupy some of them, until at least the 17th century AD.
'Preliminary research suggests that crannogs had their heyday during the Iron Age'
Surveys in Scotland have located the remains of several hundred crannogs, which vary tremendously in size, shape, date of occupation, and methods of construction. For example, some prehistoric crannogs in densely wooded areas began as freestanding houses supported on wooden stilts or piles, while those in barren areas were stone or part-timber houses supported on partly natural or entirely man-made rocky islands.
Today, they appear as tree-covered islands or as submerged stony mounds completely hidden from view. Preliminary research suggests that crannogs had their heyday during the Iron Age (c.750 BC to AD 42), which is where this study begins.
Archaeologists also know it as a period of architectural emphasis in which status, design and function influenced the construction of an extensive range of roundhouses. Many of these survive in the landscape as ephemeral circular shadows best seen as cropmarks [scottish_crannogs_fact_file.shtml#1] from the air. Hundreds more are substantial stone-walled or timber buildings, and still more are found on islands or lie submerged in lochs.
'... evidence from ring-ditches, like those at Broxmouth in East Lothian ... suggests a development towards two-storey accommodation ...'
Today we do not know much about the people who built these apparently spacious and complex structures, nor do we know why they did so. The evidence from ring-ditches, such as those at Broxmouth in East Lothian, and brochs such as Carloway in Lewis, suggests a development towards two-storey accommodation with the ground floor reserved for animals.
Built in commanding locations and towering over the landscape, these labour-intensive, material rich roundhouses would have been very imposing and visible testimony to the wealth of their owners.
In medieval times, crannogs were used not only as homes, but also as fishing stations, a place to keep hunting dogs, and especially as refuges in times of trouble. Often castles were built on islands which may have been the remains of earlier crannog dwellings, and family papers may contain valuable clues.
'... the island was granted to the monks of Scone Abbey in 1122 by Alexander I ...'
Priory Island [scottish_crannogs_fact_file.shtml#2] in Loch Tay, Perthshire (or the Isle of Loch Tay as it is also known), is one example of a clan stronghold being constructed upon earlier remains. It is recorded that the island was granted to the monks of Scone Abbey in 1122 by Alexander I, after his queen, Sybilla, reputedly died on the island. The Campbells of Glenorchy constructed a fort on the island in the 16th century, the ruin of which still stands today.
Practical search methods are also used to determine the likely presence or absence of one or more crannogs in a loch. These methods include aerial photography, remote sensing [scottish_crannogs_fact_file.shtml#3] using sonar from a boat, and snorkelling or diving to take a closer look. The landscape offers clues as well, for most crannogs were built in shallow water near good arable land.
The realisation that these mounds were the remains of ancient dwellings, inspired people such as Dr Robert Munro and the Reverend Odo Blundell to carry out limited excavations in south-west Scotland and the Highlands. They had heard of similar discoveries in Switzerland, when extremely low water levels revealed the timber stilts of an ancient village [scottish_crannogs_fact_file.shtml#4] in Lake Zurich. Reverend Blundell was the first to investigate a crannog underwater when, in 1908, he donned helmet, canvas suit and lead boots to examine Cherry Island in Loch Ness.
'Several partial excavations of crannogs were carried out between the late 19th century and the mid 20th century.'
Several partial excavations of crannogs were carried out between the late 19th century and the mid 20th century. Finds of structural timbers, artefacts and plant materials generated much public interest, and many theories about how and why these dwellings had been constructed.
Although they never reached the bottom of the mounds, the early excavators thought that the ancient builders had used stone, or rafts of timber and brushwood, to create an island, on which they built a house. Several decades later, however, in a different location, new evidence from underwater excavations presented a very different theory.
'... it was the only site where the timber stumps of a walkway survived ...'
The first ever underwater excavation of a crannog began in 1980, at Oakbank Crannog. It was chosen because it was the only site where the timber stumps of a walkway survived and organic remains were visible before excavation.
The radiocarbon date of 595BC+/-60 placed it approximately in the transition period between the Late Bronze and Early Iron Ages. Logistically it afforded good access and camping provision for a small dive team. This is where the underwater search for clues about the ancient loch-dwellers began, and teams have carried out periodic excavation there, and in other lochs, ever since.
Oakbank is a wholly submerged, large stony mound, with what appears to be an annexe, or smaller mound, attached at its western extremity. The stones are heavy and covered with slippery green algae, which makes them difficult to handle. As the rock removal is a laborious task only small areas are ‘opened’ or exposed at any one time. Part of the site is still shrouded in this stone mantle.
They soon discovered the ‘compost’ consisted of cubic meters of bracken, ferns, and other organic material. Every area cleared of stones produced the same expanse of hundreds of timbers. While some structural survival was anticipated, this far exceeded expectations.
'Most of the timbers have exceptionally well-preserved marks left by the tools used to point or shape them.'
Initially, only identify the tops of what had once been vertical supports could be ientified. Closer inspection revealed smooth tops, not sawn, consistent with erosion caused by water movement after collapse. The uprights are like giant pencils, their sharpened ends driven into the loch bed to form a circular outline, while hundreds more are driven into the organic mound to varying depths suggesting different phases of building and repair. Most of the timbers have exceptionally well-preserved marks left by the tools used to point or shape them.
As the mass of timbers was painstakingly recorded, patterns began to emerge, and constructional details such as woodworking joints. Patience was rewarded in further excavation when the removal of a mass of branches revealed a recognisable structure.
The process resembled clearing debris from a flooded building where the roof had caved in and partly washed away. A large expanse of parallel timbers was discovered - some with bark intact - with others lying across them, and a section of interwoven hazel rods. This was the floor of the roundhouse.
Many artefacts, such as a fragment of cloth and almost all of the wooden objects, are found broken or incomplete, suggesting they were simply discarded. These include a hand-carved wooden plate, wooden platters, and a broken vessel perforated with several holes.
Finding the remains of a charred wooden spoon near fragments of a burnt-encrusted pot, however, suggests an episode where the pot - possibly on fire at the time - was forcibly ejected from the house. Intact, smaller and more personal items such as polished beads, spindle whorls, a sandstone pendant and other perforated stones may have been dropped by accident.
'... laboratory analysis has identified a range of food and other plant remains known as ecofacts ...'
There was more. The mound also contains animal droppings, nuts and fruit stones amidst copious amounts of bracken, ferns and other plants not immediately recognisable underwater. From samples of this material, laboratory analysis has identified a range of food and other plant remains - known as ecofacts - including wheat and barley grains, nettle and herb fragments, and pollen from many edible plants.
These organic materials rarely survive on land sites unless there are waterlogged deposits. Timbers usually shrivel and split if they are not kept wet. Soil, dung, or droppings will crumble and fibrous materials also shrink and flake if not immersed.
The cold, dark and peaty water in which Oakbank Crannog is immersed, together with the anaerobic or oxygen-free conditions in the mound of material, means that micro-organisms which would normally attack organics do not survive. As a result, even the smallest pieces of evidence about the environment and lifestyle of the inhabitants are well preserved after more than 2,500 years.
A detailed picture of Iron Age life has been created there by the workers on the site, but there is still so much more to be discovered, as the major part of the site still awaits excavation and recording. Many questions still remain, but the team decided there was one way to answer at least one of them.
They realised that the only way to understand how our ancestors managed to build these commanding but enigmatic structures was to reconstruct one themselves - how they succeeded is told in the companion article to this one, 'Reconstructing Oakbank Crannog' (see it via the History Trail links column, right).
Published on BBC History: 2005-01-25
This article can be found on the Internet at:
http://www.bbc.co.uk/history/trail/archaeology/iron_age/scottish_crannogs_01.shtml
© British Broadcasting Corporation
For more information on copyright please refer to:
http://www.bbc.co.uk/history/about/copyright.shtml
http://www.bbc.co.uk/terms/
BBC History
http://www.bbc.co.uk/history/