A singular Roman dwelling, octagonal in ground-plan, was excavated in the year 2000, in Premià de Mar. It is a freestanding pavilion within a larger settlement called Gran Via-Can Ferrerons. It was not possible to date it archaeologically because the basement trenches did not contain any significant dating artefacts. Archaeological research undertaken into the architectural typology of the monument led us to the hypothesis that the structure is to be interpreted as late Roman luxury domestic housing. It was decided to use AMS 14C dating of the mortar in the masonry. This procedure dates the hardening of the carbonate binder in the mortar, which is the actual time of construction. We present the results of three analyses of mortar samples taken from the walls of the building. Radiocarbon dates coincide with the assumed architectural typology date, the date of the strata excavated at the site, and the date of the construction technique. These matches support the validity of the results (5th and 6th century AD).