The Fall of Babel (The Books of Babel, #4) by Josiah Bancroft

The incredible final book in the phenomenon fantasy series described as “future classics" follows one man's dangerous journey through a labyrinthine world and the mysteries he uncovers along the way. (Los Angeles Times).

"Josiah Bancroft is a magician. His books are that rare alchemy: gracefully written, deliriously imaginative, action packed, warm, witty, and thought provoking." —Madeline Miller, New York Times bestselling author of Circe

As Marat's siege engine bores through the Tower, erupting inside ringdoms and leaving chaos in its wake, Senlin can do nothing but observe the mayhem from inside the belly of the beast. Caught in a charade, Senlin desperately tries to sabotage the rampaging Hod King, even as Marat's objective grows increasingly clear. The leader of the zealots is bound for the Sphinx's lair and the unimaginable power it contains. 

In the city under glass at the Tower's summit, Adam discovers a utopia where everyone inexplicably knows the details of his past. As Adam unravels the mystery of his fame, he soon discovers the crowning ringdom conceals a much darker secret.

Aboard the State of Art, Edith and her crew adjust to the reality that Voleta has awoken from death changed. She seems to share more in common with the Red Hand now than her former self. While Edith wars for the soul of the young woman, a greater crisis looms: They will have to face Marat on unequal footing and with Senlin caught in the crossfire. 

And when the Bridge of Babel is finally opened, and the Brick Layer's true ambition revealed, neither they nor the Tower will ever be the same again.

Also by Josiah Bancroft:

The Books of Babel
Senlin Ascends
Arm of the Sphinx
The Hod King
The Fall of Babel