Surrounding all seven of Rome's famous hills, the Aurelian Walls were built in the third century by the Roman emperor Aurelian. More than 10 feet thick and about 26 feet high, they originally ran for 12 miles, protecting the 5.5-square-mile center of the city. During the fifth century, the height was almost doubled and more defensive features were added.
These impressively thick walls were used for defense for more than 1,000 years, last seeing battle in the 1800s. Because the city relied on them for defense, the structures were repaired and renovated over the years and remain in good condition today. Some sections of the wall sit next to roadways and often show up in unexpected, everyday places around Rome.