Rhodes. Greece. Partial view of the dry moat that surrounds the walls of the Old Town. Originally built as a formidable barrier to attack by the Knights, the moat is delightful place to wander and is mostly landscaped and dotted with palm trees and pines and giant old stone mortar balls litter the grounds. The old town is a UNESCO world heritage listed site and the best preserved, oldest and largest living medieval city in Europe. The 4km defensive walls were built by the Knights of St John during the 13th to 15th century to defend Western Europe against the expanding Ottoman Empire.