Fort St Elmo, Malta. It withstood Ottoman invasion in the mid 1500s, where Malta was bombarded by over 100,000 cannon ball shots during the Siege of Malta.
Ciudad Rodrigo, Spain - Ciudad Rodrigo is one of the many Spanish towns whose old town center is surrounded by city walls. The first stone was laid in the 12th century by order of Ferdinand II of León.
Angkor Wat, Cambodia. Construction started in around early 1100 AD. It started as a Hindu palace/temple, but was eventually converted to a Buddist one by 1200. As a capital city, Angkor Wat lasted barely 80 years before it started to decline after neighbouring rival sacked the city.
Bourtange, Netherlands - This walled town in the north of the Netherlands was built in 1851. The system of ramparts, walls, towers and moats is looks incredible from above.