Rhodes. Greece. Above view of the Old town of Rhodes which 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. Within the walls are a medieval warren of small alleyways and magnificent historical buildings. The island of Rhodes is the largest of the Dodecanese Island group and one of the most popular Greek Islands.