Area 9 are the Aurelian Walls. Built by the Roman emperors Aurelian and Probus between 271 and 275 CE, following a period of political and military instability for the city of Rome, the walls underwent a series of restorations during the period 279-401 CE.
The walls ran for 19 km around the city and marked the largest building project that had taken place in Rome for many decades. The project covers the stretch comprised between Porta Maggiore and the Lateran Cathedral.
The new structure incorporated pre-existing buildings, such as the section of the Aqua Claudia near Porta Maggiore (SA9.6) and the Amphitheatrum Castrense (SA3.1), cutting through the long stretch of the Circus Varianus (SA3.3 and SA3.5) that was forever lost to the imperial palace (Area 3) to which it originally belonged.
The construction of the Aurelian Walls had a massive impact on the existing road system of the Eastern Caelian, changing forever the nature of the region from suburban to urban and shaping the way people moved across the new boundary through the two openings of Porta Asinaria to the south (SA9.3) and Porta Maggiore to the East.