Far-reaching Hellenistic geographical knowledge hidden in Ptolemy’s data

The paper summarizes and discusses the main theses exposed in a previous book (L' America dimenticata, Mondadori Universita, 2013 [in Italian]) in light of more recent results. Specifically, the work addresses the problem of explaining the origin of the systematic error on longitudes in Ptolemy's Geographia and its logical relation with the reduced estimate for the dimension of the Earth there given. The thesis is sustained that, conversely to a frequently advanced conjecture, the shrinking of the dimension of the Earth is a consequence of the scale error on the longitudes, which, in turn, was originated by a misidentification of the Islands of the Blessed. The location of the Islands of the Blessed according the source of Ptolemy is identified in the Caribbean. The analysis of a passage by Pliny provides an independent and quantitative confirmation of the proposed identification, which sheds new light on possible contact among civilizations.