This volume examines one of Rome's most influential churches: the principal basilica dedicated to St Paul. Nicola Camerlenghi traces nearly two thousand years of physical transformations to the church, from before its construction in the fourth century to its reconstruction following a fire in 1823. By recounting this long history, he restores the building to its rightful place as a central, active participant in epochal political and religious shifts in Rome and across Christendom, as well as a protagonist in Western art and architectural history. Camerlenghi also examines how buildings in general trigger memories and anchor meaning, and how and why buildings endure, evolve, and remain relevant in cultural contexts far removed from the moment of their inception. At its core, Saint Paul's exemplifies the concept of building as a process, not a product: a process deeply interlinked with religion, institutions, history, cultural memory, and the arts. This study also includes state-of-the-art digital reconstructions synthesizing a wealth of historical evidence to visualize and analyze the earlier (now lost) stages of the building's history, offering glimpses into heretofore unexamined parts of its long, rich life.