Dark Ages
A term given by some to the centuries after the Roman period, from about 400 AD, when it is very difficult archaeologically to see what happened as far as settlement, farming and so on are concerned. In most of Britain, people stopped using and making pottery, ceased producing and using coins, built in wood (which has rotted away) rather than stone and, in many other ways, have denied archaeologists the wealth of inorganic and concrete evidence they are used to from the Roman centuries. The period was really very similar to the Iron Age, and so was not 'dark' at all except by comparison to the Roman period with its consumer and commercial society, which is much more like our own and which some archaeologists find more satisfying.

Daub
A crude but very effective weatherproof mix, usually made of local mud, straw and dung, used to fill the gaps between wattle, wood and thatch in buildings from the Bronze Age onwards. See also wattle and daub.

Dendrochronology
A relatively new and very exciting way of absolutely dating material from archaeological sites where wood has survived. It is based on the idea that the growth rings of trees – oak has so far been studied – vary from year to year according to weather conditions, and that patterns of greater and lesser growth can be compared from tree to tree and from area to area. By working backward from surviving trees, from timbers in old houses and in even earlier churches, and from timbers from excavated sites, a 'master chronology' can be built up. Any timber discovered in buildings or in waterlogged deposits (with anaerobic conditions) can then be compared with the growth rings already known. If the outer rings of the tree or the sapwood are present, a very precise date can be suggested for when the tree was felled. As most wood in the past seems to have been worked and used 'green', such a date will be very close to that of the construction of the feature under investigation. See also augering.

Diatom analysis
Diatoms are tiny unicellular algae, which live in water. Their silica cell walls are often preserved in large quantities in rivers, lakes or formerly wet habitats. Different species are found in different conditions, which means that it is possible to reconstruct past environments by studying their remains. For example, there are distinct salt-water and fresh-water species. This means that past tide levels can accurately be identified, providing invaluable information about river navigation, ports and harbours in the past.

DMV
Jargon used by medieval settlement archaeologists for 'deserted medieval villages' – that is, those settlements that have been abandoned and where only earthworks remain to indicate where the former houses and farmsteads once stood. Some of these villages disappeared in the 15th century when a lot of arable land was put down to grass; a few disappeared as a result of the Black Death and other plagues in the 14th century; but most were just slowly abandoned as economic activity changed and people drifted away to new occupations elsewhere. Many are not medieval in origin but Saxon (or earlier) and were not abandoned in the Middle Ages but in the 16th, 17th or 18th centuries. In practice, few villages were ever completely deserted; there is usually at least a church, farm or few cottages left. And very many so-called DMVs were never actually 'villages' – ie they were never large settlements with their own churches and manor houses.

DNA profiling
DNA profiling was first used to identify criminals. Now it is an important tool in forensic archaeology, used to identify individuals, such as the Romanovs and also to gain information about people in the past. DNA is the genetic material found in every cell of every living thing. The DNA molecule is a double helix – it looks like a ladder that has been twisted into a spiral. The uprights are the same for everyone, but the sequence of the rungs is unique for each person, apart from identical twins. Forensic scientists use enzymes to cut the DNA into short pieces, and these fragments vary in length, depending on the individual's genetic code. The fragments are separated according to their size, using an electric current, then they are labelled with a radioactive substance. An X-ray of the labelled fragments produces a 'DNA fingerprint' that looks rather like a bar code.

The DNA from the cell nucleus is fragile and can be difficult to read if the samples come from very old bodies. But another, more stable, form of DNA is found in the mitochondria – the structures that produce the cell's energy. Mitochondrial DNA is harder to test and can only indicate relationships through the maternal line, but it provides important information about archaeological finds. DNA in the Y-chromosone (which determines the male sex) can also be used to identify relationships between men.

DNA: tracing relationships between people in the past
DNA profiling is becoming increasingly important archaeologically in helping to trace the relationships between different people in the past. We each inherit our DNA from our parents. Most of it gets mixed up in a process called 'recombination' before being passed onto us. Two parts of our genetic make-up, however, are passed on entirely from one parent or the other, so they don't go through the recombination process.

The first is mitochondrial DNA, which is inherited almost entirely from our mothers. (There is actually one mitochondrion in a sperm, but for most practical purposes this can be discounted in tracing genetic relationships.) The second is the Y chromosone, which determines the male sex and is inherited entirely from our fathers.

Differences in the genetic sequences of mitochondrial DNA and Y-chromosonal DNA – known as polymorphisms – can be identified and tracked back through generations. So, for example, we know that if two people have polymorphism A, they are descended from the same ancestor.

This has allowed researchers to work out two things about our ancestry:

1. That we all have a female ancestor in common (known as the 'mitochondrial Eve'); and
2. That all men have a male ancestor in common (known as the 'Y-chromosonal Adam').

Researchers have calculated that both 'Adam' and 'Eve' lived in Africa somewhere between 100,000 and 200,000 years ago. This doesn't mean that they knew each other; they could have lived many thousands of years apart. But it does mean that everyone alive today (or at least everyone whose DNA has so far been examined) is descended from 'Eve' and that all men alive today are descended from 'Adam'.

Documents
A catch-all for the mass of paperwork (and parchments) produced, particularly in the Middle Ages and later, as part of the bureaucratic processes of government. Nearly all documents are of interest in discovering something about life in the past, and very many categories of document are essential for a full appreciation of what went on. See, for example, the Anglo-Saxon Chronicle and the Burghal Hidage.

Dugouts
A rough-and-ready term for boats constructed from single logs that have been hollowed out using axes, adzes and fire. Also called logboats.

Dykes
Earthworks usually made up of one or more sets of banks and ditches, often running across country and frequently intended to block unrestricted passage across the landscape. Originally they may have been topped with timber palisades, and may have had deeper ditches and steeper banks, which have been eroded over the years. Good examples include Offa's Dyke along the Welsh border, Bokerley Dyke in Dorset and the Wansdyke in Wiltshire.