Castel del Monte, Apulia, Italy

© Toni Spagone/Alam

An octagonal architectural gem

Built in the 1240s by Holy Roman Emperor Frederick II, Castel del Monte (Castle of the Mount) in Apulia, south-east Italy, has an unusual octagonal design. Eight stone walls stretch between eight octagonal towers and enclose an octagonal courtyard. Each of the two floors also has eight trapezoidal rooms. Acclaimed and protected as a World Heritage Site in 1996, the castle reflects a harmonious integration of classical Roman, Arabic and medieval architecture and design. To some, its octagonal symmetry suggests a connection between Heaven and Earth.

It's not clear why it was built. Without a drawbridge, moat or curtain wall to protect it, it was clearly not a defensive fortress, and its lack of stables call into question its function as a hunting lodge. Over the centuries it has served as a prison and as a refuge from the plague. But whatever the emperor’s intention, he left a captivating monument that still enchants today.