The borders of modern France are roughly the same as those of ancient Gaul, which was inhabited by Celtic Gauls. Gaul was conquered by Julius Caesar in the 1st century BC. Christianity took root in the 2nd century and 3rd century AD, and became so firmly established by the fourth and fifth centuries that St. Jerome wrote that Gaul was the only region free from heresy. In the Middle Ages, the French would adopt this as a justification for calling themselves "the Most-Christian Kingdom of France". In the 4th century AD, Gaul's eastern frontier along the Rhine was overrun by Germanic tribes, principally the Franks, from whom the ancient name of "Francie" was derived. The modern name "France" derives from the name of the feudal domain of the Capetian Kings of France around Paris. Existence as a separate entity began with the Treaty of Verdun (843), with the division of Charlemagne's Carolingian empire into East Francia, Middle Francia and Western Francia. Western Francia approximated the area occupied by modern France. In 1337 a growing disupute over the succession of the French grown escalated into a war beteen England and France which would go on for more than a century and become known as the Hundred Years War. In 1430 the Hundred Years War is still raging and England begins the game with control of three territories that were historically a part of France. The Dutchy of Burgundy has played both sides in the conflict, but has largely allied with the English to France's detriment. France's two most likely allies are Scotland and the Holy Roman Empire (Germany), though should Burgundy be convinced to turn against the English, they could make a useful ally as well. Aragon, to France's south, also has the potential to be a pivotal player in the Hundred Years War, helping France to drive England out of the south of France or causing France to lose any hope of holding its own position there. France begins play with a fair force of knights and those mark an extremely potent advantage that the French player should not squander lightly.