As most other cities in the old days Rome was also a fortified city with walls protecting them from intruders. As the city grew, they always needed to construct new walls according to the size of the city. Because of this the old walls were often torn apart, and today few old city walls can be seen. If you would still like to see some old city walls, the Aurelian walls can be seen. If you travel to the metro stop Piramide (line B) some leftovers from the walls built between year 271 and 275 AD can be seen. They are worth a visit, and while in the area, do not miss out on the Gaius Cestius pyramid, also in the area.
The Aurelian wall has an entrance fee and it costs 9 Euro for adults. It is open from 9.00 – 18.00 every day, except on Tuesdays.