The itinerary extends for 3.2 km from Porta Nomentana to the ancient locality of “ad Spem Veterem” (at the Vecchia Speranza [Old Hope]), corresponding to the area of Porta Maggiore and a prime entry point to the city of the Roman aqueducts.
The route changes direction several times and is almost flat, with the exception of the section of Via di Porta Labicana, which descends slightly from Via Tiburtina down to the valley at Via dello Scalo di San Lorenzo.
In this sector the walls form a border or backdrop to various urban landscapes: from the airy ones of the 19th-century boulevards (Viale del Policlinico and Viale Pretoriano), to the romantic ones of Villa Gentili, sometimes providing a counterpoint to the solid rationalist architecture, as in the case of the Termini station visible from Via di Porta San Lorenzo.
The presence of public complexes, such as the Castro Pretorio barracks, the National Library and the Air Force Headquarters, prevents the full visibility of both elevations of the Walls. On the contrary, in the section between Via dei Frentani and Via Tiburtina, it is possible to appreciate the interior and exterior façades, although sometimes masked by later alterations that conceal the original elevations.
The needs of an expanding city that had recently been made a capital led to the demolition of several sections of the Walls between the end of the 19th century and the 1930s: this is the case with the numerous openings created to connect the university city and the district of San Lorenzo to the centre (especially between Viale dell’Università and Via Tiburtina), and the demolitions necessary for the expansion of the Termini station along Via di Porta Labicana.
From Viale Pretoriano it is possible to access a 150-metre-long stretch of walkway, transformed in the 18th century into a roof garden in the annex of Villa Gentili, a rare example of a dwelling built above the Walls.