This article describes the on-site conservation of 12 polychrome floor mosaics found in a 3rd-cent. A.D public building in Zippori, Israel. The intervention is part of a broader project directed by the National Parks Authority of Israel, and includes the construction of fixed architectural roofing, the consequent temporary protection of the mosaics and sealing the trenches left from the removal of the original masonry walls. The conservation work was carried out allowing the public to watch the work "live". This paper describes the treatments on the mosaics and comments on various aspects. Starting with technical procedures, we will then consider the principles and the objectives behind the choice of the methods followed and we will conclude with some general reflections.