For the next five hundred years, there was much interaction between the two regions, as both Britain and France were under Roman rule. After the fall of the Western Roman Empire, this was followed by another five hundred years with very little interaction between the two, as both were invaded by different Germanic tribes. Anglo-Saxonism rose from a mixture of Brythonism and Scandinavian immigration in Britain to conquer the Picts and Gaels. France saw intermixture with and partial conquest by Germanic tribes such as the Salian Franks to create the Frankish kingdoms. Christianity as a religion spread through all areas involved during this period, replacing the Germanic, Celtic and pre-Celtic forms of worship. The deeds of chieftains in this period would produce the legendaria around King Arthur and Camelot – now believed to be a legend based on the deeds of many early medieval British chieftains – and the more historically verifiable Charlemagne, the Frankish chieftain who founded the Holy Roman Empire throughout much of Western Europe. At the turn of the second millennium, the British Isles were primarily involved with the Scandinavian world, while France's main foreign relationship was with the Holy Roman Empire.