What the field is, and what it is not
Maritime archaeology is the study of human contact with the sea through physical remains. It includes shipwrecks, but also harbours, jetties, fish traps, drowned prehistoric landscapes, abandoned hulks on foreshores and the cargo and belongings that ships carried. Archaeologists working on land and underwater share the same aim: to understand people in the past from what they left behind, and to record a site properly before it is changed.
That last point separates the discipline from treasure hunting. A wreck is a closed collection, a snapshot of a ship and its cargo at one moment. Once objects are lifted without record, the relationships between them are lost, and with them much of what the site could have said about trade, shipbuilding and life on board.
A short history of the discipline
Divers have recovered objects from wrecks for centuries, but systematic work is much more recent. The aqualung, developed in the 1940s by Jacques Cousteau and Emile Gagnan, gave divers real freedom of movement, and by the 1950s and 1960s archaeologists were learning to dive. A frequently cited milestone is the excavation of a Late Bronze Age wreck at Cape Gelidonya, off southern Turkey, in 1960, directed by Peter Throckmorton and George Bass. It showed that a seabed site could be excavated to the same standards as a land site. Bass later helped found the Institute of Nautical Archaeology in the 1970s, which went on to work on wrecks such as the Uluburun shipwreck.
Large projects also brought public attention. The Swedish warship raised in 1961, described in the story of the Vasa warship, and the Tudor ship raised in 1982, covered in the Mary Rose wreck article, showed what could be learned when a whole hull survived.
Finding a site
Many wrecks are first reported by fishermen whose nets snag, by sponge divers or by sport divers. Others are found deliberately, through survey:
- Documentary research. Records of losses, logbooks, insurance files and old charts narrow down where to look.
- Side-scan sonar. Sound pulses create an image of the seabed and show shapes standing out from it.
- Magnetometers. These detect iron, such as anchors, cannon or fastenings, even when buried.
- Sub-bottom profilers. These look beneath the sediment for buried objects or hull remains.
- Remotely operated vehicles. Cameras and manipulators allow inspection of sites too deep for divers.
A signal is only a lead. Natural rock, modern debris and old cables can look similar until someone examines the spot directly, which is why a wreck’s identity often takes years to establish.
Recording and excavating
Once a site is located, the first task is to record it as it lies. Teams usually establish a fixed reference point and measure the position of every feature from it, drawing plans and taking photographs. Photogrammetry, which builds three-dimensional models from many overlapping images, is now a common way of documenting a site without touching it.
Excavation is slow and expensive. Divers fan away or gently suction sediment, label and lift objects, and note exactly where each one was found. Time underwater is limited, so large projects can need thousands of dives spread over several seasons. Increasingly, archaeologists prefer to leave a site undisturbed on the seabed when it is stable. This is called preservation in situ, and it is often the most responsible choice, because excavation is a one-way process.
What survives, and why
The sea is not uniformly destructive. In shallow, oxygen-rich water, timber is quickly eaten by wood-boring organisms such as shipworm, and often only the lower hull or the heavy cargo remains. Where a hull sinks into soft, oxygen-poor mud, the buried part may be sealed from decay and survive remarkably well. The cold, brackish Baltic is a famous example, since shipworm does not thrive there, which is part of the reason the Vasa and several other wrecks are so complete.
Because the survival is so uneven, archaeologists must be careful about drawing wide conclusions. A cargo of amphoras tells us what a ship carried at the end of one voyage, not everything it ever traded.
Interpreting the evidence
Fieldwork is only the start. The timbers show how the ship was built, which connects to wider questions about ancient shipbuilding methods. Tool marks, repairs and the choice of wood suggest the skills and resources available to the builder. Dendrochronology, which dates wood by comparing tree-ring patterns, can sometimes show when and where the timber grew. Radiocarbon dating helps where tree rings cannot.
The cargo and the ship’s equipment reveal trade and daily life: what was bought and sold, what the crew ate, which tools and weapons they carried. Scattered over a wide area, the same evidence can also show how a ship broke up. Some wrecks have been central to understanding events as different as the Batavia wreck of 1629 off Western Australia and the discovery in 1985 of the Titanic sinking site on the North Atlantic floor, though the aims and ethics of work on a recent disaster site differ from those of a Bronze Age excavation.
Conservation
Waterlogged wood looks solid, but its cell structure has often been replaced by water. If it dries out unprotected, it can shrink and crack badly. Conservators therefore keep finds wet and then slowly replace the water with a supporting material, historically often polyethylene glycol, before controlled drying. Metals, leather, rope and ceramics each need their own treatment, and some large hulls have taken years of spraying and treatment. This cost is one reason many projects choose not to raise a wreck at all.
Law and ethics
Wrecks sit in a tangle of ownership, salvage rights and national law. Traditional wreck salvage rules were designed to reward people who saved ships and cargo, not to protect archaeology. In response, many countries now have heritage laws, and the 2001 UNESCO Convention on the Protection of the Underwater Cultural Heritage set out principles against commercial exploitation of sites. How far such rules apply varies from place to place, and disputes between governments, salvors and museums continue.
The lasting value of the field is that it fills gaps in the written record. Many of the most famous shipwrecks are known because someone survived to tell the story, but the far more numerous ordinary losses, such as small coasters and trading vessels, left no account at all, and archaeology is often the only way to meet them.