The purpose of illustration is to record the things we find, whether they are excavated layers, artefacts or structures, so that written descriptions make more sense and the information is preserved for the future. Artefacts can be photographed and studied at length in a museum, so these are not usually illustrated on site. However, the layers, features and structures uncovered during an excavation may only be visible for a short time when the excavation is happening, and it is vital to make an accurate and permanent illustrative record of them. Every context must be included in a plan or section and photographed – however insignificant. It may turn out to be much more important than it first seems, once post-excavation analysis has been carried out.