Classical Latin appears to be without regional dialects, yet Latin evolved in little more than a millennium into a variety of different languages (the Romance languages: Italian, French, Spanish, Portuguese etc.). Was regional diversity apparent from the earliest times, obscured perhaps by the standardisation of writing, or did some catastrophic event in late antiquity cause the language to vary? These questions have long intrigued Latinists and Romance philologists, struck by the apparent uniformity of Latin alongside the variety of Romance. This book establishes that Latin was never geographically uniform. The changing patterns of diversity and the determinants of variation are examined from the time of the early inscriptions of Italy, through to late antiquity and the beginnings of the Romance dialects in the western Roman provinces. This is the most comprehensive treatment ever undertaken of the regional diversification of Latin throughout its history in the Roman period.