Antonio Manetti reconstructed Hell as a straight cone with a vertex angle of 60°. The cone section is an equilateral triangle, and the arc of the Earth’s surface forming the base of the cone is the sixth part of the meridian circle. Having established this geometric shape, and using 20,400 miles as the measure of the Earth’s circumference (Convivio III v 11), Manetti calculated that the meridian arc forming the base of the cone was equal to 3,400 miles. Dividing the circumference “by three and one-seventh [3.14],” he found the diameter of Hell to be 6,490 miles and its depth 3,245 miles. In his lectures at the Accademia Fiorentina (1587-1588), Galileo (1564-1642) defended Manetti’s figures against Alessandro Vellutello (1473-?), who argued that Hell was only 295 miles deep.