Which Greek inspired Mercator and Columbus?

The Greek philosopher Ptolemy inspired both Gerardus Mercator and Christopher Columbus through his works on geography and cartography. Ptolemy's "Geographia" provided a systematic approach to mapping the world, incorporating latitude and longitude, which influenced Mercator's development of the cylindrical map projection. Columbus, on the other hand, used Ptolemy's ideas to estimate distances on his voyages, believing he could reach Asia by sailing west from Europe.