The Italian Dominican Ptolemy of Lucca (ca. 1240-1327) figures among the most significant political theoreticians of the Middle Ages. In his De regimine principum (ca. 1300), a continuation of Thomas Aquinas’ De regno, Ptolemy paints a highly original picture of civil happiness. Taking the Roman Republic as his model, Ptolemy praises the “political” government that is presented as a sufficient condition for felicitas civilis, and this through the virtue of its citizens, the balance of its forces, and the harmonious and active collaboration of the various groups that constitute the community.