This book is the first in-depth analysis of one of the most remarkable monuments of Ostia, the ancient port town of Rome: The Domus del Ninfeo (III, VI, 1-3). Originally built as a multi-storey complex during the reign of Hadrian, in Late Antiquity it was converted into a ground-floor mansion to serve the dominus and his extended family. During this phase the building was enriched with marble floors and the elegant nymphaeum that gives it its current name. This study aims to present a comprehensive picture of the Domus, analysing not only the many structural changes but also its topographical setting, historical context and social inferences. The text also features the archaeological drawings that were made during the study and the results of a clearance in an area of the house previously neglected; the latter has provided invaluable evidence for interesting structural modifications that were previously completely unknown.