All gates of the Aurelian Wall of Rome still stood at the end of the XIX century, more or less restored through time. Three of these – Porta Ostiensis, Appia, and Tiburtina – presented a supplementary gate aside. No particular attention has been paid by scholars to these so-called posterulae, and only sketchy descriptions exist of them. Even Lanciani, who devoted much time to the study of the Wall, quoted only incidentally their chronology (Fifteenth century) and the reason of their existence, as gates strictly functional to the passage of pilgrims; however, he did not investigate further who decided to build these posterulae and when they were later closed. Historical maps of Rome never depict them, apart for Nolli’s Eighteenth century map, where they are marked by an asterisk, thus indicating that they were closed with masonry. The posterula near Porta Ostiensis disappeared under a bombing in World War II; the one near Porta Appia still retains its frame and shutting; and the one near Porta Tiburtina was reopened in 1873. By comparing the remains and the ancient pictures of the posterulae with similar architectures in Rome and scrutinizing historical documents relating to the building activity of the popes in the Fifteenth and Sixteenth centuries, the author argues that the posterulae were most probably build under pope Alexander the 6 th in occasion of the jubilee of 1500, as transit points for pigrims directed to the main basilicas of the suburbs (San Sebastiano, San Paolo and San Lorenzo), in order to gain the special indulgence for the Holy Year. In this case, the subsequent closing of the supplementary gates might have occurred been immediately after the jubilee, as previously planned, in order to restore the defensive system of the Wall.
