Sir William, a prominent Knight Templar, spent 50 years researching and planning his cathedral. A cross-section of the building shows it was designed on the basis of the octagon, the hexagon and the triangle enclosed within a circle, these being some of the fundamental patterns of sacred geometry. What we see today is only the choir of the planned much larger cruciform building.

William St Clair was a very learned man, an illuminatus, and he used his vast library of oriental Gnostic and cabbalistic teachings as inspiration for the design of the building and of the carvings he wanted to incorporate into Rosslyn. He built the village of Roslin to house the many artisans he invited to help in the building work. These included many from Europe and the East as well as local tradesmen.

The carvings include Judaic, Celtic, Norse, Templar and Masonic symbols as well as Christian images. This plethora of signs and symbols from many cultures may in part be attributed to the ethnic origins of the stonemasons involved in its creation as well as to the ideas of Sir William, but it also makes Rosslyn unique and earns it its local nickname, the Cathedral of Codes.

Symbols and signs have been used to communicate for millennia. While scholars could read and write often in more than one language, the layman/peasant was usually illiterate. Images or symbols then took the place of literature for the masses. As a means of communication, images are especially effective when those concerned, as has been mentioned, may not be literate or who speak a different language.

This form of communication can be multi-levelled, multi-layered and the meanings can change over time. For example, the fish had many meanings in early Christianity. It was the first symbol of Christian identity - 'fishers of men'. Also, the equal-sided cross, a pagan symbol representing the balance of nature, didn't become an identifying Christian symbol until the 4th or 5th century when the upright was lengthened to represent Jesus' Crucifixion. In antiquity, the balanced cross was also known as the Mark of Cain. According to the bible, it is a sacred symbol created for the people by the Lord and was worn by the people to protect them from Jehovah's wrath. The Mark of Cain is a Red Equal-Sided Cross, like the "Celtic Cross" or the "Rosy Cross", and was chosen as the main symbol of the Knights Templar.

Also, huge changes took place during the Reformation, which would have changed the meanings of many of the symbols.