There’s been a bit of talk in the news lately about walls, a “cutting-edge” technology that has been used for more than 10,000 years and that is older than the wheel.

In our travels throughout the world, we’ve seen many examples of walls, both old and new. Their purpose has been to keep people out (or, in some cases, in). Several are memorialized with fascinating museums that convey the mind-set that went into building these structures.

Seoul, South Korea: Construction on Hanyangdoseong, the Seoul City Wall, commenced in 1396 and features four main gates. The wall follows the natural contours of the steep hills that ring South Korea’s capital city. The aptly named Seoul City Wall Museum, next to the ancient Heunginjimun Gate, preserves the history of this remarkable landmark. Despite the 20-foot height of the wall, one of the scale models in the museum shows someone climbing it, effectively negating its effect. Hikers can download the Seoul City Wall app that will guide them along the 12-mile swath of remaining walls. The detailed map highlights each segment along with miles walked, sights to see along the way, and even calories burned.

Rome, Italy: The Museo delle Mura (Museum of the Walls) is along the Aurelian walls of the city that were constructed between A.D. 270 and 275 to defend against barbarian hordes from Northern Europe. The wall was 12 miles long and 21 feet tall. At this free museum, at the San Sebastiano Gate on the Appian Way, visitors can stroll atop the walls and take in exhibits about the wall’s history.

Berlin, Germany: A notorious wall that was built relatively recently, the Berlin Wall famously encircled East Berlin; given its outsize role in 20th-century history, it’s hard to believe it stood for only 28 years. Despite the heavily armed “death strip” along its path, intrepid East Germans were able to tunnel under, swim around, scramble over, or even soar above it in homemade hot-air balloons. At the Berlin Wall Memorial on Bernauer Strasse, a section of the wall that was left more or less intact now serves as a poignant reminder of the Cold War separation of the city. The adjacent museum records the history of this ill-fated barrier.

Whether they’re several millennia old or were built in our lifetime, these walls became obsolete. Yet they provide an intriguing perspective on the concept of borders and security throughout history. One wonders which contemporary walls will be reduced to museum status in the future.

Philadelphia natives Larissa and Michael Milne have been full-time global nomads since 2011. Pick up more travel tips on their travel blog at ChangesInLongitude.com