In the Archive of Colonna family at monastery of Santa Scolastica in Subiaco (Rome) is preserved the last letter that Justus Lipsius, philosopher and professor from University of Louvain, wrote to cardinal Ascanio Colonna in the first of March 1606. The letter is published for the first time and is written in order to express gratitude because the roman cardinal had accepted Philip Rubens, the favourite pupil of Lipsius, as librarian. The letter describes the moral and intellectual skills of Philip Rubens, typical expertise of the neo-stoic ideal of lifestyle. Philip shared the prototype of virtuous existence with his younger brother Peter Paul, with which was living in Rome until the death of their mother. The self-control in opposition of the adversities and the deep affection for friends and family are the fundamental precepts of Seneca thought. Justus Lipsius published the "opera omnia" of roman philosopher with his commentaries and sent it to Ascanio Colonna, as the letter reports.