The Emperor Aurelian ordered in 271 the building of a fortified wall around Rome
(the Aurelian Wall) meant for the protection of the City against any attack.
It had a perimeter of about 19 km and circled almost the entire City.
The wall was built in bricks and reached at some places a height of 10 m.
You can see a part of it alongside the Tiber by the Campus Martius.
The Aurelian Wall as it goes along the Tiber by the Mausoleum of Augustus.
The Aurelian Wall as it reaches the Porta Portuensis.