en.wikipedia.org/wiki/The_Path_to_Rome

The place named here is Porta del Popolo (formerly Porta Flaminia). Official Rome tourism materials identify Porta del Popolo as a gate built under Emperor Aurelian, and the official page for the Aurelian Walls says those walls still surround Rome’s historic centre and include the stretch at Piazzale Flaminio, where Porta del Popolo stands. By contrast, the official Rome page for the Passetto di Borgo describes the Vatican Walls as a separate fortified structure running from the Apostolic Palace toward Castel Sant’Angelo.

So the article is conflating two different fortification systems: Porta del Popolo belongs to Rome’s Aurelian Walls, not to the Vatican walls.

This number is mislabeled. Bibliographic records for the 1902 edition separate the Library of Congress classification from the LCCN:

• Open Library lists Classifications: Library of Congress D919 .B44 1902
• and separately Edition Identifiers: LCCN 02015369.

So 02015369 is not the LC class; it is the Library of Congress Control Number. The LC class/call number for this edition is D919 .B44 1902.