Infra-red
False-colour photography, particularly with infra-red film that registers differences in heat loss from the ground, has been used to try to locate archaeological sites.

Inhumation
Literally, a burial in a grave. The term is used archaeologically to distinguish between inhumations or circumstances in which bodies are laid out on the surface.

Insects
A category of biological information which environmental archaeologists can use, where there are remains, to work out what the environment was like in the past. See also beetles and environmental archaeology.

Interglacial
A period of warmer climate between glacials or 'Ice Ages'. The area of ancient human activity expanded during interglacials and contracted during glacials.

Iron Age
The Iron Age is the period from about 700 BC to 43 AD – following the Bronze Age and before the Roman period – when the working and use of iron gradually becomes evident. It is characterised in Britain by the construction of large fortified hillforts and the full exploitation of the landscape with numerous farmsteads and extensive field systems. The hillforts may be connected with invasions by Celtic peoples from Europe.