Over the centuries, definite articles in Romance languages have expanded their use to include generic, collective, and abstract nouns, essentially becoming noun markers. This usage is not confined to just a few languages, either, but is found in most, if not all, Romance languages, major and minor. This thesis examines the question of how this came to be, whether through diffusion from one language to all others, or through independent parallel development. I first trace the history of definite articles in three major Romance languages, French, Spanish, and Italian, starting with the emergence of the definite article in Late Latin as it derived from Classic Latin demonstratives. It includes an analysis of the use of definite articles in six works of literature, one in each language from the late thirteenth century, and one in each language from around the year 1500. The results show definite articles were used more frequently than expected in the earlier Spanish work, perhaps hinting at diffusion from Spain. Nevertheless, placing these results in historical context, I argue that this use arose through independent parallel development through the process that gave birth to definite articles in the first place - grammaticalization.