At a time when Europeans still longed to be Roman and were just learning to be Christian, two extraordinary holy women-Genovefa of Paris (ca. 420-502) and Brigit of Kildare (ca. 450-524)-began to roam their homelands. One of these saints raised an apostolic church in the imperial city that would become Paris. The other scavenged fragments of that dwindling empire for the foundations of a grand Roman basilica built deep in barbarian territory. Both...