We come now to Fort Mifflin's river-facing side, in this case the southwest. Noting the sudden difference in building materials, I came up with the brilliant theory that, on the sides of the fort most likely to be fired upon by naval artillery, granite was used; while for the rest of the fort, it was more inexpensive brick. I came to this logical conclusion because I hadn't bothered to read any of Fort Mifflin's many informational signs, which made it clear that the riverward side of the fort was the original, 1772 construction (granite), while the rest of the wall wasn't completed until after 1778, with brick.