The boundary between the Neogene and Quaternary (Anthropogene) Systems has been the subject of discussion for many years. Its position has been discussed at almost all INQUA congresses since 1932 (2d International Conference, Association for Study of Quaternary Period in Europe, Leningrad), as well as at international geological congresses. At the 28th Session of IGC held at London (1948) it was proposed to draw the boundary between the Pliocene and Pleistocene at the first signs of climatic cooling in the marine section of the Italian Neogene. Calabrian marine deposits include the first appearance of northern immigrants in their faunas and their stratigraphical continental analogue, the Villafranchian, was adopted as the basal member of the Pleistocene. The 29th Session f IGC held in Algeria (1952) approved the resolutions of the 28th IGC.

At the 5th INQUA Congress at Madrid and Barcelona (1957) the Subcommission on the Pliocene-Pleistocene boundary was organized under the Commission on Nomenclature and Stratigraphy of the Quaternary. The Subcommission has submitted recommendations to every subsequent INQUA Congress but these were not approved by the Sessions of the International Geological Congress.

In 1972, the International Colloquium on the lower boundary of the Quaternary organized by the INQUA Subcommission was held in the Soviet Union. Decisions made at this Colloquium were approved at the 24th International Geological Congress held in Canada in 1972. These recommendations confirmed a proposal submitted to the 28th International Congress that Italy be the stratotype area for the boundary between the Neogene and Quaternary Systems, and the original definition that the base of the Pleistocene should be drawn in marine deposits at the lowermost level in the section at La Castella, Catanzaro, where Hyalinea baltica is recognized. In addition, the 1972 International Colloquium changed the correlation of the Calabrian with the subdivisions or biozones of Villafranchian c ntinental deposits because, as proved by subsequent studies, the lower Villafranchian corresponds to the Astian, not the Calabrian. Where Calabrian analogues cannot be established easily, it was decided to use local subdivisions based on established stratotypes.