Former megacity lies in ruins. Those ruins are, however, surrounded by towering walls.

Less famous than Hadrian's Wall.

Was another massive frontier erected by the Romans. Dating back to AD142, the fortification was commissioned by the emperor, Antoninus Pius, Hadrian’s successor, and was built largely of turf and wood.

The most famous wall of all, this gargantuan structure is also perhaps the most beautiful. It clocks in at 13, 171 miles long.

This ancient limestone barricade once formed part of an important Jewish temple. The holiest place where Jews are permitted to pray.

The most famous wall of all, this gargantuan structure is also perhaps the most beautiful. It clocks in at 13, 171 miles long,

Was once the capital of the Inca Empire and comprised a series of walls, which, legend has it, were laid out to look like a puma’s snarling teeth.

The second longest wall in Europe after Hadrian’s. Constructed to protect Dubrovnik and its nearby salt pans.

73-mile long wall, which dates back to AD122, remains the world’s largest Roman artefact. The crumbling remains are often cloaked in fog, and also mystery.

Was a major city in ancient Mesopotamia and was famously protected from invading armies by its eponymous walls, which were long considered to be impenetrable. Made of blue glazed tiles and featuring bas-relief dragons the walls have been ravaged by conflict, neglect and plundering over the years.

That fragments of this wall can now be bought from souvenir shops across the country's capital. The stretches of wall that remain today offer a fascinating insight into a once-divided capital.

The legendary city was made famous in Homer’s epic poem, the Iliad.