1. The Alhambra

The Alhambra is the greatest example of Islamic military architecture in Europe. Sultan Muhammad I constructed this ingenious, impregnable fortress in 1238 amid treacherous political betrayals.

2. Istanbul's Hagia Sophia

Fiery Roman Emperor Justinian ordered the rebuilding of the great church of Hagia Sophia in Istanbul almost 1500 years ago. Modern science now uncovers the secret to this vast golden dome's longevity.

3. Petra

Carved into the side of a narrow gorge in the unforgiving deserts of Petra in modern day Jordan, the ancient Nabataeans turned engineering on its head to create their glorious royal city, Khazneh.

4. St. Paul's Cathedral

From the ashes of London's Great Fire in 1666 rises Christopher Wren's daring architectural vision. As England's first Baroque cathedral, St Paul's is an icon to rival the grandeur of ancient Rome.

6. Machu Picchu

Built using techniques that surpass modern ones, the temples, altars and residences of Machu Picchu have resisted torrential rains, landslides and earth tremors since being abandoned by the Incas.