In 1603, at the age of eighteen, Cesi invited three slightly older friends, the Dutch physician Johannes van Heeck (in Italy Giovanni Ecchio), and two fellow Umbrians, mathematician Francesco Stelluti of Fabriano and polymath Anastasio de Filiis of Terni to join with him in the founding of the Accademia dei Lincei ("Academy of the Lynxes"), aimed at the understanding of all natural sciences through a method of research based upon observation, experiment, and the inductive method. Their goal was to penetrate the secrets of nature, observing it at both microscopic and macroscopic levels. The four men chose the name "Lincei" (lynx) from Giambattista della Porta's book "Magia Naturalis", which had an illustration of the fabled cat on the cover and the words "...with lynx like eyes, examining those things which manifest themselves, so that having observed them, he may zealously use them".[4] Cesi chose the sharp eyed lynx and the eagle for the Academy's symbols.