The Siege of Thebes recounts the catastrophic conflict between the brothers Eteocles and Polynices, whose struggle for the throne of Thebes leads to the total destruction of their city. Lydgate presents this narrative as a continuation of Chaucer’s Canterbury Tales, framing the story as a tale told by the Monk while the pilgrims are on the road. The protagonist’s objective is to secure his rightful claim to the throne, but he is thwarted by his brother’s betrayal and the inevitable weight of ancestral curses. The narrative utilizes a formal, courtly style to explore the political instability and moral decay inherent in dynastic warfare.

Readers and scholars often examine this work for its historical significance as a bridge between Chaucerian tradition and later medieval literary developments. Discussion frequently centers on Lydgate’s ability to adapt classical Greek tragedy into the framework of a medieval pilgrimage narrative. Critics highlight the poem's dense, formal language and its preoccupation with the instability of political power during the fifteenth century. The text is noted for its atmospheric descriptions of the siege, which provide insight into the period's understanding of ancient warfare and moral philosophy.