What is an important motif in the novel, The Valley of Fear?

One important theme in the novel, The Valley of Fear, is that of encirclement, which illustrates Douglas’ endeavor to escape entrapment by the Scowrers. This motif is illustrated in a number of different ways, namely the moat surrounding Douglas' home, the triangle inscribed within a circle, Douglas’ wedding ring, and the “valley of fear” which is located in a sunken area, which is encircled by mountains.