Before Pompeii was under Roman jurisdiction, a high stone wall was erected around the city. Except on the frontier, no cities in the Roman Empire needed walls to protect their citizens. There were no formidable enemies of local governments during the first century thanks to Augustus, the Roman ruler who had brought peace to the Empire (Pax Romana). Emperor between 27 B.C. and 14 A.D., it was Caesar Augustus who was in power when the Prince of Peace was born in Bethlehem. With no safety advantage to living inside the walls, residents of Pompeii began living outside the walls, even converting the walls into living quarters and businesses. The house above is known as the Suburban Villa of Porta Marina.
In the Western Hemisphere we generally don't understand the New Testament writers' concept of walls. Americans think of walls as structures to keep someone inside, such as "behind prison walls." The walls around a city in any century had been built to keep enemies out, not its own citizens inside. Consider the Apostle Paul's statement that Christ "has broken down the middle wall of separation" (Ephesians 2:14). In context, we see that there had existed a spiritual "wall" around the Jews, protecting them from the lawlessness of the Gentiles. Once Christ's blood was shed, He offered peace to all men so that the "wall" no longer served any purpose. It was similar to Rome's protection of its citizens, making a city wall unnecessary. As this relates to the Jews, consider that this metaphorical wall was never built to keep Jews inside, but was only for keeping their spiritual enemies outside. Jesus Christ offered peaceful coexistence for all people.