The Lord of the Rings is a deeply symbolic and metaphorical work throughout; space here allows for only a brief overview of a few major motifs. Readers will note and develop the significance of others.
The very title of this second volume of Tolkien's novel (see prefatory matter in the Summary and Analysis) invites us to think metaphorically about the book. Although Tolkien opposed, on artistic grounds, the division of his story into three volumes, he nevertheless chose the title The Two Towers for the published form of Books III and IV. He did, however, acknowledge its ambiguity: "[I]t might refer to Isengard and Barad-dr, or to Minas Tirith and Barad-dr; or Isengard and Cirith Ungol" (Letters, p. 170). He eventually seems to have decided for himself that the title refers to Orthanc (Saruman's tower within Isengard) and Cirith Ungol, in which case the two towers of the title are metaphors for the power of evil. Several passages in the text itself bear out this interpretation: clearly, the description of Isengard and Orthanc in mechanistic, dehumanized terms in Book III, Chapter 8, for instance, leaves no doubt that this once beautiful place has become a stronghold of evil. Towers can, however, also be toppled; and that same passage suggests the inherent "nothingness" of evil-it is powerful, to be sure, but it is not substantive. Saruman fancies himself a powerful man because of the way in which he has transformed Isengard and its tower, but he is doomed to be a puppet of Sauron.
Similarly, Sauron has transformed his towers of Minas Morgul and Cirith Ungol into dark places-but the light from the Phial of Galadriel shines brightly when Sam and Frodo shine it at the close of Book IV: "[N]ow a star had descended into the very earth" (Book IV, Chapter 9). (The motif of a star descending to earth, by the way, comes from old Norse mythology and was most likely Tolkien's initial inspiration, as a young man, for creating his entire Middle-earth mythology; see Humphrey Carpenter's biography of Tolkien for details.) Readers would do well to note other metaphorical uses of darkness and light in the text-for instance, Gandalf's arrival with reinforcements at Helm's Deep as a new day dawns in Book III, Chapter 7; or the fact that Gollum cannot abide to travel in the daytime throughout Book IV-which fact resonates with Tolkien's Christian understanding of "darkness" as a metaphor for evil-see, e.g., John 3:20-21 and 13:30. But readers need not be religious, of course, to appreciate how Tolkien appreciates this near-universal symbolism of light and darkness for his story.
The Eye of Sauron became a very literal presence in director Peter Jackson's film adaptation of The Lord of the Rings, but careful readers of The Two Towers will note that it is a metaphor of Sauron's heavy and oppressive, wide-ranging gaze in Tolkien's actual text. They will also note the recurrence of eyes as a metaphorical motif in the book; for example, the references to Shelob by her eyes alone in Book IV, Chapter 9. The palantr into which Pippin looks in Book III, Chapter 11 further reinforces the image of, in a sense, "the evil eye." The eye is a powerful and haunting motif for evil in Tolkien's narrative; the fact, however, that its gaze is limited (as Gollum knows, since he is able to discover a secret way into Mordor) and that Sauron very often misdirects its gaze (for example, paying more attention to the coming battle at Minas Tirith than on the passage of Cirith Ungol) gives hope that evil can be overcome.
The Ents are actual characters in Book III, of course, but they also serve a metaphorical purpose. As stated in the Summary and Analysis, the Ents represent Tolkien's deep love and concern for the natural world. As Tolkien wrote in one of his letters, "I am (obviously) much in love with plants and above all trees, and always have been; and I find human maltreatment of them as hard to bear as some find ill-treatment of animals" (Letters, p. 220). Tolkien was apparently inspired by a line in Shakespeare's Macbeth to create the literal image of a forest marching to war on a castle; but the image is symbolic in that it represents the natural world rebelling against the unnatural, mechanized, industrial order which humanity has attempted to impose upon it. The conflict between these two orders-the natural and unnatural, the organic and synthetic-is never far from the surface of the symbolism in The Lord of the Rings.