The presence of human settlement in the territory of Aveiro extends to the period associated with the great dolmens of pre-history, which exist in most of the region. The Latinised toponym ‘'Averius'’ derived from the Celtic word aber (river-mouth, etym.< Brythonic *aber < Proto-Celtic *adberos, compare Welsh Aberystwyth).
For a long period Aveiro was an important economic link in the production of salt and commercial shipping. It was a centre of salt exploration by the Romans and trade centre through the Middle-ages, registered since 26 January 959 (from the testament of Countess Mumadona Dias to the cenóbio of Guimarães). During this testament, Mumadona Dias also highlighted the ancient name for Aveiro, this time referring to the monastery's lands in Alauario et Salinas, literally, "a gathering place or preserve of birds and of great salt".