Woodcut of a "stone extracted from a pastry cook of Montargis" from Des Monstres et prodiges by Ambroise Par矇, 1573. Des Monstres is filled with unsubstantiated accounts of sea devils, marine sows, and monstrous animals with human faces. With its extensive discussion of reproduction and illustrations of birth defects, the book invited accusations of pornography. A kidney stone, also known as a renal calculus, is a solid concretion or crystal aggregation formed in the kidneys from dietary minerals in the urine. The existence of kidney stones was first recorded thousands of years ago, and lithotomy for the removal of stones is one of the earliest known surgical procedures. Medical texts from ancient Mesopotamia, India, China, Persia, Greece, and Rome all mentioned calculous disease. The Roman medical treatise De Medicina by Aulus Cornelius Celsus contained a description of lithotomy, and this work served as the basis for this procedure until the 18th century. New techniques in lithotomy began to emerge starting in 1520, but the operation remained risky. In 1901, a stone discovered in the pelvis of an ancient Egyptian mummy was dated to 4,800 BC.