This is a reminder that many citrus fruit used to have insanely thick peels, the way some pomelos do:
An early-modern ode to citrus fruit – in pictures
Johann Christoph Volkamer was a 17th -century Nuremberg silk merchant with passion for gardening that defined his life. He was obsessed with citrus fruit at a time when the genus was largely unknown in northern Europe. In 1708, he commissioned 256 plates of 170 varieties of the fruit – images collected in a new book by Prof Iris Lauterbach called JC Volkamer.