Abstract: Where is Mount Purgatory? How high is it? How large is the island upon which it was situated? In the
nineteenth century Rodolfo Benini and Ideale Capasso developed a series of hypotheses and calculations to find
answers to these questions. Each used data derived from mathematics, astronomy, history of science and
cartography, but they completely disagreed on the location and on the overall size and shape of the island. In this
paper we review the main points of these two scholars, then we rework the calculations and estimates, according to
a new astronomical hypothesis presented by Giulio Magli and Claudio Facciolo
