The Paris souterrain is a recurring motif that presents a hidden, subversive reality existing in parallel to the oppressive world on the surface. For characters in both timelines, these ancient quarries, catacombs, and tunnels function as a physical and symbolic realm where memory, resistance, and freedom are possible. Initially, Kristof and Alesander explore the underground as an escape from the anxieties of Nazi occupation, seeing it as a historical curiosity. However, the space transforms into a serious strategic asset as Alesander begins mapping it for the Resistance, creating a fortified bunker and escape routes. The tunnels become the literal embodiment of the theme of The Physical and Conceptual “Underground” as a Space for Resistance, providing a tangible path to safety for Sasha and the other Jewish teenagers. Similarly, in the 17th-century plotline, the sewer tunnels beneath the Salpêtrière offer Alouette, Marguerite, and Sylvine a difficult but viable path to freedom. 

The souterrain also serves as an archive of defiance, its walls marked with revolutionary slogans and ancient carvings. Sasha recognizes this legacy when she notes, “It’s so quiet here. You can almost hear the stories being whispered from the walls” (331). Her observation confirms that the underground is a living repository of history, offering inspiration and guidance to those who fight for their lives in the present.

Alouette’s uniquely crafted blue dye is a symbol of female genius, creative agency, and a legacy of knowledge that survives patriarchal oppression. This symbol draws on the secret, oral nature of female knowledge and transmission in history, which has often been ignored, belittled, or suppressed, and considered transgressive or occult in its threat to patriarchal knowledge structures. The blue dye represents Alouette’s refusal to be constrained by the guild’s laws, which dictate that women can only serve, not create. The color’s brilliance is a visual manifestation of her intellect and ambition, a secret she fiercely guards as her own. Its existence incites the greed and suspicion that lead to her father’s arrest and her own imprisonment, symbolizing the perils often faced by women who act with agency and express their abilities. As her secret, the formula for the dye remains Alouette’s inalienable property, a piece of knowledge that cannot stolen from her mind. When, in the Epilogue, the secret of “Skylark blue” is revealed to have been passed down through generations of women, this continuation reflects the alternative matriarchal patterns of female knowledge transmission in history. Using it in stained-glass window for Notre-Dame, her female descendant sees the color as knowledge “passed from mother to daughter like a thread too precious to break” (445). This confirms the dye’s meaning as proof of how art and culture as means to preserve memory and identity, making Alouette’s rebellious creativity a lasting, if private, part of history.