Octagon is two-dimensional polygon, enclosed by eight straight line segments. We can see the use of octagons in traditional art and architecture. 
The Castel Del Monte, the 13th century castle and citadel in Southern Italy used an octagonal plan in the castle design. This castle includes an octagonal core in the centre. It also has an inner octagonal courtyard which is again surrounded by 8 octagonal towers. Octagonal patterns were also used in Roman mosaic and tile patterns in ancient palaces, churches etc. For example, Jerusalem's Dome of the Rock, San Vitale Church in Ravenna (20th century), and Alhambra Palace, Spain.