According to the Castel del Monte Wikipedia page, “historians have debated the purpose of the building and it has been suggested that it was intended as a hunting lodge. Another theory is that the octagon is an intermediate symbol between a square (representing the earth) and a circle (representing the sky). Frederick II may have been inspired to build to this shape by either the Dome of the Rock in Jerusalem, which he had seen during the Sixth Crusade, or by the Palace Chapel of Aachen Cathedral.”
There also seems to be some controversy as to whether or not Castel del Monte was a Knights Templar castle. Looking a little deeper into Castel del Monte, I found it interesting that the structure isn’t aligned to the four cardinal points (north, south, east and west), but is several degrees west of north, just like the Dome of the Rock. From what I can tell at this time, Aachen Cathedral; when viewing it via Google Earth, appears to be aligned with the four cardinal points. This had me leaning more towards the Dome of the Rock aka Al-Aqsa mosque, as the inspiration for the design of Castel del Monte.
After locating several good quality diagrams of the building design for Castel del Monte, I noticed that it looked very similar to not only the Dome of the Rock, but also the veil template, which plays a very important role in my recently published book Jesse James and the Lost Templar Treasure, in which I describe how the treasure template I call the veil template, matches not only the design of the Dome of the Rock but also it’s orientation, which is several degrees west of north.
Knowing the treasure legends, the maps and templates I had discovered tie back through Freemasonry, Rosicrucians and others back to the Knights Templar, this has me leaning even more towards the possibility that the Castel del Monte could have also served as a Templar castle.
While I’m not certain of a connection between the Knights Templar and Castel del Monte, it wouldn’t shock me and in light of the information I provided above, a connection between the Templar and Castel del Monte seems all the more likely. I personally believe it was designed after the Dome of the Rock aka Al-Aqsa mosque.
In addition to the information above, I will leave you with this video from the website of The Rosicrucian Order, AMORC, which also hints (strongly) at a connection between the Castel del Monte and the Knights Templar.