The need for the protection,recording and study of monuments is gradually developed in the 19^th century as material documents of the past. In dealing with monuments, either the stylistic restoration or anti-restoration movement are developed, two extreme positions, with more tranquil tendencies which appear especially by the end of the century. In the 20^th century the need for the protection of monuments matures and the restorations pass from the experimental to a scientific stage. Scientific research is systematically used to the restoration projects, where historical and aesthetic value is recognized. At the same time, the meaning of the monument is expanded to include works of art of later historic periods, together with their surrounding space, as well as whole sites.

Having deep knowledge of the theories of the past and those of his period, Cesare Brandi formulated his theory of conservation, the first completely developed theory in the area. He dealt with meanings such as material and the potential unity of a work of art, lacuna, patina, ruins, time and space and their relevance to the conservation and the way the last takes into account the historical and artistic value. He also introduced preventive restoration. In his theory he formulated two axioms that determine the character of the restorations. According to these axioms, only the material of the work of art should be maintained and the restoration should aim at its potential unity. In general, a critical approach is necessary to define what should be preserved or removed and the way lacunae is completed in order to avoid a historical or artistic falsification. The role of the context of a monument is emphasized, whose preservation is just as essential. The principals of conservation referred to works of art apply to architecture as well, where the relation between monument and context is more crucial.

Brandi’s theory, though heavily criticized, was widely and internationally adopted, and provided the foundations for the Venice Charter, which is still in force. The Greek participation at the congress for the Venice Charter and mainly the studies of Greek architects abroad and especially at ICR, where Brandi was director for many years, contributed to the diffusion of his theory in Greece, where restoration was till then dominated by empiricism and stylistic approach. Nevertheless, the scientific approach in conservation was guaranteed only after 1975, when the Venice Charter was officially adopted and started gradually to be applied.