Final answer:
Early Celtic oral stories reached France through the Celtic expansion across Europe and were preserved through the region's transition from Roman to Frankish rule. The blending of cultures allowed these stories to become part of French society, and they were eventually recorded in writing as literacy increased.
Step-by-step explanation:
The early Celtic oral stories were transmitted by the Celtic people who had expanded across Europe from around 450 BCE. These stories were part of an oral tradition where information and cultural narratives were passed down verbally through generations. With the Celts' expansion, including into the region we now call France during this time, their stories would have naturally disseminated among the local populations. Furthermore, after the fall of the Roman Empire, Germanic tribes such as the Franks took over the region, further mixing cultures and traditions. As the Franks, including their Merovingian leaders like Clovis I, established the foundations of what would become modern France, they absorbed the local customs and stories, including those of the earlier Celtic inhabitants.
The process of these stories reaching France was a result of successive waves of migration, conquest, and settlement. This cultural blend is best encapsulated by the transition from Roman Gaul to Frankish rule, where despite shifting political powers, the narratives and customs of the Celtic people persisted and eventually became embedded into the fabric of French society. Later, as literacy spread and the recording of history became more prevalent, these tales found their way into written records, allowing a wider and more durable propagation of what were originally oral epics.