Castle walls were an evolutionary defense structure over a period of thousands of years. They served to protect the inhabitants of strategic millitary outposts , which would often result in cottage industries popping up around the outpost to serve the needs of every day life behind the castle walls. Castle walls are seen in all cultures, from Mesopotamian, to Arabian, and to (most famously) western european cultures.

Castle walls initially started out as a wall of vertical logs around a hill top or cliff side, with crude huts or buildings inside. These provided poor defense capabilities as they were not very durable and needed constant maintanence. As siege technologies improved, so did castle wall construction and complexity. Castle walls eventually reached the state they are now, which is the block and rubble style. The block and rubble style consists of two parallel walls of thick stone and concrete filled with the rubble and dirt created by the construction and quarrying needed for the main walls. These walls were often three feet thick, but could be over twelve feet thick in the most crucial areas.

Although castle walls initially started out as a round circle of logs, but with the advent of stone wall construction, it was easier to build walls in neat, straight lines and 90 degree corners to create a box shape that was also appealing to the eye. This style of castle wall was rapidly ditched in lieu of more advanced cyndrillical towers being placed upon each corner. The problem with 90 degree corners is that to the attacker, they are the most vulnerable part of the castle and easiest to knock down or weaken. For the defender, it is difficult to defend these corners as arrow slits , or narrow vertical windows, cannot be easily placed directly on the corner, creating a large blind spot. Rounded towers serve a triple purpose; 1) less construction materials are needed overall for the staircase due to spiral construction, 2) The wall's primary weakness is removed, 3) Blind spots are eliminated and improves visibility for the archer by allowing more arrow slits to be placed on the corners.