By Colin Martin
Last updated 2011-02-17
It is not just the land that reveals hidden secrets of past times but the sea offers wonderfully preserved treasures. This is the story of how archaeology went underwater, the difficulties they face and the problem of restoring often very fragile finds.
For the archaeologist on land, the main dangers come from land developers. The marine archaeologist, however, must beware of the sea as they try to preserve shipwrecks from the pounding waves. Each fragile wreck is a unique time capsule of our past: encrusted cannons, ancient wine bottles and other historical treasures. Treasures that the sea is loath to give up. This is the story of underwater archaeology.
Alexander the Great is reputed to have gone down in a diving bell...
Those involved in a shipwreck may lose everything in the catastrophe, including perhaps their lives. But the remains of sunken vessels and their contents, even if broken up and scattered, provide future generations with unique windows into the past. Each site represents a moment frozen in time, and every item recovered from it is part of a vast three-dimensional archaeological jigsaw. Archaeologists know they can never complete it, but by analysing the evidence they find, and fitting it into the jigsaw's framework, they come ever closer to their goal of constructing a true picture of the ship before it became a wreck. Each has a special story to tell, and is therefore a fragile and irreplaceable microcosm of its times.
Diving on sunken ships has happened throughout history. Alexander the Great is reputed to have gone down in a diving bell, while Roman urinatores (free divers) apparently salvaged cargo from a wreck 20m deep off the south of France.
The aqualung opened the underwater world to diving adventurers like Hans Hass and Jacques Cousteau in the 1940s. Although many ancient wrecks were found, little thought was given to their archaeological significance. It was not until 1960 that a young archaeologist, George Bass, teamed up with explorer Peter Throckmorton to investigate a Bronze Age shipwreck at Cape Gelidonya in Turkey. Bass learned to dive and showed that archaeology could be done underwater to the same standards as on land. Bass's team is now excavating a Bronze Age shipwreck of the 14th century BC at Uluburun off Turkey.Since then techniques have been refined, but the principles remain unchanged. Many classical wrecks have been investigated in the Mediterranean, such as the Roman wine carrier with 6000 amphoras off Madrague de Giens near Marseilles.
Underwater archaeologists working around the British Isles have investigated several wrecks of the Spanish Armada, such as the Girona off Antrim and La Trinidad Valencera off Donegal. The biggest project has been the excavation and raising of Henry VIII's battleship, Mary Rose which sank in the Solent in 1545. The largely intact hull of the Dutch East Indiaman 'Amsterdam' was found off the English town of Hastings. The boat had been swallowed into the sand when she had beached there in 1748. The wreck has been the focus of investigations for 30 years now. Current projects include the Swan, a small Cromwellian warship, which was lost off the west of Scotland in 1653.
Notice to visitors at a wreck site
 ©
Well-preserved wrecks abound in the Baltic, where low salinity and cold water slow down decay. These include the Vasa, which sank on her maiden voyage in 1628 and was raised from Stockholm Harbour in 1961. Another is the Kronan, which blew up and sank during a battle with the Dutch in 1676. Not all wrecks are now under water. Many have been found in reclaimed parts of Holland's Zuider Zee, after the land has been drained. At Skuldelev in Denmark a group of five Viking ships, sunk to form a blockage at the entrance to a fjord.
Having survived for centuries in this state, they will probably remain in much the same condition for centuries to come.
Although they have to work in a hostile environment, underwater archaeologists follow the same principles as their counterparts on land. A site must first be surveyed. This is done with tape-measures and grids using simple geometry, supplemented by photography, video, and geophysics. The aim is to produce an analytical map so that the wreck can be assessed. Often this will enable archaeologists to record the site and interpret its significance without having to disturb it. Only in exceptional cases are historic shipwrecks excavated, and their contents recovered.
Well-preserved wrecks have usually reached a state of equilibrium with their environments. Having survived for centuries in this state, they will probably remain in much the same condition for centuries to come. But if they are disturbed, the stability which has protected them will be broken. Archaeologists normally excavate shipwrecks only if they are under some kind of threat - a shift in the environmental balance, perhaps, or plans to dredge a harbour entrance where historic sites are known to lie. An example of this kind of 'rescue' excavation is provided by the Cromwellian warship Swan wrecked in 1653 off Mull, which is now threatened by seabed erosion.
Very occasionally archaeologists excavate wrecks which are not under threat to recover them and their contents for public exhibition. Examples of these include the Swedish warship Vasa at Stockholm (1628) and the Mary Rose at Portsmouth (1545). In such cases the damage to their archaeological integrity is offset by careful records made by the archaeologists, the conservation of the ships and their contents, and subsequent publication and display.
Parts of the hull tell the marine archaeologist how the ship was designed and built. Tool-marks reveal woodworking techniques used by the shipwrights. Fragments of rigging and rope - sometimes even pieces of sails - help to show how the ship was operated by its crew. Other finds throw light on activities such as navigation, medical care, everyday crafts, food storage, cooking, and domestic routines. If the ship was a merchant vessel parts of its cargo may have survived, perhaps revealing where it came from. Warships contain evidence of the weapons they carried. Above all, items of clothing and personal possessions bring us into immediate contact with people who lived and died long ago.
Divers make their way up from the seabed
 ©
Archaeology is often associated with the discovery of human remains, and skeletons are sometimes found in shipwrecks. Such material is of especial interest, since the individuals concerned are predominantly healthy young males. They are a group not normally found in burials on land which naturally tend to be of people who are either old or diseased.
...shows that sixteenth-century English archers were routinely drawing weights greater than those achieved by modern Olympic athletes
Several skeletons from the Mary Rose (1545) were identified as archers from the unusual development of their wrist, arm, shoulder, and back muscles caused by repeated practice with the longbow from early youth. This evidence, together with examples of the bows themselves, shows that sixteenth-century English archers were routinely drawing weights greater than those achieved by modern Olympic athletes! A skeleton from the Cromwellian warship Swan, wrecked in 1653, reveals that although this individual's legs were relatively poorly developed, and bowed from rickets in childhood, his arms and shoulders were exceptionally strongly muscled. This identifies him as a seaman, used to hauling on ropes and other activities involving his upper body.
Such finds are relatively rare, for even on wrecks where there is heavy loss of life most of those who perish drown in the sea while trying to escape. An exception was the loss of the Swedish warship Kronan. It capsized, blew up, and sank in 1676, trapping most of her 850-strong crew before she went down. Hundreds of skeletons have been found in the wreck. Many show evidence of deep sword-cuts, apparently inflicted by officers desperately attempting to establish discipline amid the unimaginable terror and chaos inside the doomed ship.
Human bones are an important source of scientific evidence about the past. At the same time they are the remains of fellow beings, reminding us of our own mortality and demanding proper respect. After study it is appropriate that they should be laid to rest.
Recovered artefact
 ©
Although the sea sometimes preserves archaeological material in almost miraculous condition, it remains fragile and unstable. Once brought to the surface, and exposed to air and light, objects degrade with alarming rapidity. Iron corrodes so quickly that an item may become too hot to touch before cracking into pieces from internal pressure generated by chemical change. Wooden objects, which may look as good as new when taken out of the water, split and collapse if allowed to dry out. Items recovered from the sea must therefore be given conservation treatment from the moment they reach the surface.
An iron gun, for example, can be attached to a sacrificial block of zinc.
Conservation involves stabilising and consolidating objects without changing their character or structure. Metals are often treated by electrolysis, which reverses corrosion by linking them to an anode. This operates much on the principle of an electric battery and stabilises one metal at the expense of another 'sacrificial' one. This can be done in the laboratory, although large metal objects are sometimes treated while still on the sea bed. An iron gun, for example, can be attached to a sacrificial block of zinc. The seawater providing a natural electrolyte between the two metals.
Materials with once-living cells like wood, leather, bone, or fibre require a different kind of treatment. Since much of their structure is broken down and replaced by water, objects made from these materials usually retain their original appearance, though they are fragile and will collapse if the water dries out. They can be conserved by replacing the water with a more durable material, which strengthens the object and allows it to keep its shape. By immersing the object in water, and gradually introducing a 'consolidant' chemical such as polyethylene glycol, the cellular structure of the material is reinforced. This, to the point, at which it can be removed from the water and allowed to dry. Freeze drying is another method which can be used.
Small objects can be treated quickly and economically in the laboratory. Larger items - such as the hull of a ship - are more complicated and take longer. The Vasa took many years to conserve by keeping the wooden hull under a constant spray of water and gradually introducing consolidant into it. After several decades the process is complete, and the restored ship is now Sweden's prime tourist attraction.
A restored watch
 ©
Contrary to popular belief, most historic shipwrecks do not contain 'treasure'. Only a very few ships in the past - notably the galleons which brought consignments of bullion from the New World to Spain, and the Indiamen which took chests of money and precious metals to the far East to purchase return cargoes of spices - carried large quantities of coins and ingots of gold or silver. The wrecks of such ships have inevitably been targets for treasure-seekers.
The real treasures which lie beneath our oceans are the time-capsules of the past.
This had led to disagreements between the treasure hunters and archaeologists over the future of these wrecks. However, the debate goes beyond the vociferous and frequently acrimonious arguments of these diametrically-opposed interests. In the last analysis, this issue is one which can only be decided by individual nations, working in concert with the world community at large.
Yet, the value of most historic shipwrecks can never be measured in monetary terms. The real treasures which lie beneath our oceans are the time-capsules of the past. It is the aim of marine archaeology to unlock them.
Courses and Wreck Diving
If you are interested in becoming involved with marine archaeology, then the Nautical Archaeology Society (NAS) offers divers a chance to become involved with wreck investigation. The wrecks of two protected 17th Century warships in the Sound of Mull - the Swan and the Dartmouth - can be visited by divers by arrangement with the NAS Training Officer at the Lochaline Diving Centre in Scotland.
The NAS runs a variety of practical courses ranging from a basic introduction to nautical archaeology to the skills of surveying, drawing, and taking photographs above or below the water. More advanced techniques which can be learned include the use of equipment such as magnetometers, side-scan sonar, and remotely operated vehicles (ROVs). The NAS can be contacted on 023 9281 8419.
There are number of wrecks in British waters which are designated as historic wrecks. These may not be dived except under licence. The Historic Wreck map shows the location of some protected wrecks around Britain such as the Swan and the Dartmouth.
If you are interested in wreck diving, the details of all known wrecks around the British Isles - over 60,000 - are contained in a computer data base at the UK Hydrographic Office in Somerset. A free brochure about wrecks is available from their Wreck Section. They can supply details such as the name, tonnage, date of sinking and depth of wreck of any vessel sunk since 1913. This is provided that the latitude and longitude of the wreck is known in accordance with the Admiralty chart. A fee is charged which depends on the research that may be involved. Please contact them for further details. Another useful source on wreck diving is the divernet site which is listed in our links section.
´óÏó´«Ã½ © 2014 The ´óÏó´«Ã½ is not responsible for the content of external sites. Read more.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.
