This thesis presents a commentary on the first 253 lines of book 4 of Lucan's epic poem, the Pharsalia, and is split into four parts. Part one forms the main introduction, which outlines the methodology and focus of the commentary; there the question of Lucan's 'epicness' is posed, and the plus quam motif of the poem is related to the passage under discussion. Also contained in part one are sections on the structural format of the commentary, a review of particularly important scholarship, a brief discussion of Lucan's style, and notes on the text. The remaining three parts of the thesis form the commentary proper: each section of commentary is prefaced with an introductory discussion, which outlines key events and themes in that segment of the episode, and discusses Lucan's interaction with a particular type of literature. The introduction to part two is primarily concerned with Lucan's use and/or abuse of historical sources. It compares the version of the episode at Herda provided by Lucan with that narrated by Caesar in his account of the Civil War, and suggests possibilities for differences between the two (such as Lucan's characterization of Caesar). It then briefly outlines the other extant sources which refer to the Herda conflict. and considers the question of whether Lucan was responding directly to Caesar's account, or whether there may have been an intermediary source (such as Livy). The commentary on lines 1-47 follow. The introduction to part three assesses Lucan's response to didactic and philosophical texts. It argues that an underlying dialogue with Virgil's Georgics can be found throughout the episode at Herda, and that this intertextual relationship is established in order to contrast the destructive civil war behaviour of the soldiers with the productive agricultural activity which they could be undertaking. Another section of the introduction considers the similarities between Lucan's deluge scene and those found in Ovid's Metamorphoses and Seneca's Natural Questions. It proposes that Lucan alludes to the cataclysmic imagery of these texts in order to suggest a new world order, which is then undermined when the post-deluvian world is proven to be worse than that which went before. The commentary on lines 48-143 follow. The introduction to part four argues that Lucan deliberately underpins the fraternization scene with the imagery of love, sex and marriage, and that his decision to end the scene with a mass slaughter forms part of a wider concern linking sex, marriage and death within the Pharsalia. It assesses the importance of Concordia as a goddess in social, political and philosophical terms, and concludes that her presence may imply that the kinsmen are in some way participating in a pseudo-marriage ceremony. The commentary on lines 143-253 follow. The commentary demonstrates that throughout the Herda episode Lucan engages with a wide range of texts, and that his decision to respond to genres which are not 'traditionally' epic shows him both as an inheritor of Virgil and Ovid's style of multilayered epic, and as an author pushing the boundaries of epic poetics.