Before an excavation begins, the working area must be prepared. Certain points are marked on the surface, for safety and in order to map the site. The area on the sea bottom is marked off and divided into small areas or squares which are numbered for reference and for locating objects found on the site.
Underwater excavation begins with the removal of deposits covering the site. For this a suction hose is usually used, which aspirates the sediments and helps to clean the archaeological remains. Sometimes a water jet or water curtain is used.
As archaeological material appears, it is cleaned, labelled and its position noted. Digging is done gradually through levels or layers until the lowest level is reached. Each level is recorded and documented graphically and in photographs before any material is removed. It is very important to do all these tasks systematically and carefully to avoid losing information which can never be recovered. This ensures a good archaeological record, enabling the found materials to be interpreted and their historical meaning to be evaluated.