Architect and mathematician; first to suggest entasis in Greek buildings. Pennethorne was the son of Thomas Pennethorne. He joined the architectural firm of John Nash (1752-1835) where he quickly became Nash's favorite pupil. In 1830 he toured Europe in order to study the architectural monuments. While in Athens in 1832 he observed that the lines of the Parthenon were not the strict rectilinear ones, but were in fact bent to make the building appear more even from a distance. He observed similar configurations at a temple in Thebes.