In 1890, Cajal published a paper (Sobre la existencia de células nerviosas especiales en la primera capa de las circunvoluciones cerebrales. Gaceta médica catalana, nº 23: 737-739) reporting the existence of special nerve cells in the first layer of the cerebral cortex of lower mammals. He called them special because they had a unique peculiarity: they had two or more axons. Soon after, Gustav Retzius described the same cells in higher mammals and primates. Since then, they have been known as Cajal-Retzius cells. Today it is known that they are the first cell population to appear in the developing cerebral cortex and their importance in the stratification of this structure, through the secretion of the reelin protein. 3D model by Jeremy Swan based on an original illustration by Santiago Ramon y Cajal Courtesy of the Cajal Institute, Spanish National Research Council or CSIC©