This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book explores how religious rhetoric shaped the institutions of the early medieval city. The populous and renowned Roman city of Aquileia offers a unique lens to study how the urban environment changed from that of a traditional Roman city to a "Christian" one over the course of the fourth and fifth centuries. The book provides the historical background necessary for a work on Aquileia and its environment. The history of the city up to 400, along with the layout of the city based on the archaeological record, necessarily shapes the changes that took place over the tenure of Chromatius's life. It explores the issue of ethnic identity and rhetoric by considering the language surrounding barbarians in Chromatius's preaching. The book focuses on the ethnic dialogue to examine Chromatius's direct attacks on the Jewish community in Aquileia.