Aconcio later wrote that he became attracted to the ideas of the Reformation while in service to Landriano. He knew that it was dangerous to express these beliefs openly while living in Italy and decided to pursue a career in military engineering that would allow him to live safely in exile. He taught himself the basics of engineering through conversations with military men like Landriano and Giovanni Maria Olgiati. He also took careful note of fortifications he had the opportunity to visit while traveling through Europe.